Ethereum has two account types:

Externally-owned – controlled by anyone with the private keys
Contract – a smart contract deployed to the network, controlled by code. Learn about smart contracts
Both account types have the ability to:

Receive, hold and send ETH and tokens
Interact with deployed smart contracts
Key differences

For creating contract -
Creating an account has a cost because you're using network storage
Can only send transactions in response to receiving a transaction
Transactions from an external account to a contract account can trigger code which can execute many different actions, such as transfering tokens or even creating a new contract
thereum accounts have four fields:

nonce – a counter that indicates the number of transactions sent from the account. This ensures transactions are only processed once. In a contract account, this number represents the number of contracts created by the account
balance – the number of wei owned by this address. Wei is a denomination of ETH and there are 1e+18 wei per ETH.
codeHash – this hash refers to the code of an account on the Ethereum virtual machine (EVM). Contract accounts have code fragments programmed in that can perform different operations. This EVM code gets executed if the account gets a message call. It cannot be changed unlike the other account fields. All such code fragments are contained in the state database under their corresponding hashes for later retrieval. This hash value is known as a codeHash. For externally owned accounts, the codeHash field is the hash of an empty string.
storageRoot – Sometimes known as a storage hash. A 256-bit hash of the root node of a Merkle Patricia trie that encodes the storage contents of the account (a mapping between 256-bit integer values), encoded into the trie as a mapping from the Keccak 256-bit hash of the 256-bit integer keys to the RLP-encoded 256-bit integer values. This trie encodes the hash of the storage contents of this account, and is empty by default.
An account is made up of a cryptographic pair of keys: public and private. They help prove that a transaction was actually signed by the sender and prevent forgeries. Your private key is what you use to sign transactions, so it grants you custody over the funds associated with your account. You never really hold cryptocurrency, you hold private keys – the funds are always on Ethereum's ledger.

This prevents malicious actors from broadcasting fake transactions because you can always verify the sender of a transaction.

If Alice wants to send ether from her own account to Bob’s account, Alice needs to create a transaction request and send it out to the network for verification. Ethereum’s usage of public-key cryptography ensures that Alice can prove that she originally initiated the transaction request. Without cryptographic mechanisms, a malicious adversary Eve could simply publicly broadcast a request that looks something like “send 5 ETH from Alice’s account to Eve’s account,” and no one would be able to verify that it didn’t come from Alice
It is possible to derive new public keys from your private key but you cannot derive a private key from public keys. This means it's vital to keep a private key safe and, as the name suggests, PRIVATE.

There's a booming crypto economy out there, where you can lend, borrow, long/short, earn interest, and more. Crypto-savvy Argentinians have used DeFi to escape crippling inflation. Companies have started streaming their employees their wages in real time. Some folks have even taken out and paid off loans worth millions of dollars without the need for any personal identification.

Some people aren't granted access to set up a bank account or use financial services.
Lack of access to financial services can prevent people from being employable. Financial services can block you from getting paid. A hidden charge of financial services is your personal data. Governments and centralized institutions can close down markets at will.
Trading hours often limited to business hours of specific time zone. Money transfers can take days due to internal human processes. There's a premium to financial services because intermediary institutions need their cut.

Stable coins are built on top of ethereum.
Lenders can contribute in a pool from which borrowers can borrow - borrowing can be done along with keeping privacy - NFTs are often used as a collateral.

Flash loans - are currently in an experimental stage. They let one borrow without collateral or providing personal information.It works on the basis that the loan is taken out and paid back within the same transaction. If it can't be paid back, the transaction reverts as if nothing ever happened. This means a lot of logic must be included in a very bespoke transaction. A simple example might be someone using a flash loan to borrow as much of an asset at one price so they can sell it on a different exchange where the price is higher.

Lending rates are apparently much higher with stablecoins even compared to normal fiat currencies.

No-loss lotteries- The prize pool is generated by all the interest generated by lending the ticket deposits like in the lending example above. If one doesn't win this time their balance gets carried to the next round. One can withdraw at any time. Winner gets the whole prize pool.

Advanced trading - Taking money out of the exchanges and ability to access global liquidity.

Ways to grow portfolio -
There are fund management products (investment dapps) on Ethereum that will try to grow your portfolio based on a strategy of your choice. This is automatic, open to everyone, and doesn't need a human manager taking a cut of your profits.

A good example is the DeFi Pulse Index fund (DPI). This is a fund that rebalances automatically to ensure your portfolio always includes the top DeFi tokens by market capitalisation. You never have to manage any of the details and you can withdraw from the fund whenever you like.

As a platform for crowdfunding - Crowdfunding dapps are used. The expenditure can also be tracked and money can be returned if a minimum milestone is not met.

Quadratic funding -
quadratic funding. This has the potential to improve the way we fund all types of public goods in the future. Quadratic funding makes sure that the projects that receive the most funding are those with the most unique demand. In other words, projects that stand to improve the lives of the most people. Here's how it works:

There is a matching pool of funds donated.
A round of public funding starts.
People can signal their demand for a project by donating some money.
Once the round is over, the matching pool is distributed to projects. Those with the most unique demand get the highest amount from the matching pool.
^ This for me means that the governments can start prioritizing on some projects actually tracking public demand at every step.

You can think of DeFi in layers:

The blockchain – Ethereum contains the transaction history and state of accounts.
The assets – ETH and the other tokens (currencies).
The protocols – smart contracts that provide the functionality, for example a service that allows for decentralized lending of assets.
The applications – the products we use to manage and access the protocols.

Content creators can sell their work anywhere and can access a global market. Creators rely on the infrastructure and distribution of the platforms they use. These are often subject to terms of use and geographical restrictions.
Creators can retain ownership rights over their own work, and claim resale royalties directly.

Use cases - ticketing, in-game items, real estate, digital artworks, domain names, in the future it is possible that your car or house is also a NFT that you can only open if you can prove the ownership rights.

ethereum.eth - ENS service to register & manage a NFT domain

And if you create an NFT:
You can easily prove you're the creator.
You determine the scarcity.
You can earn royalties every time it's sold.
You can sell it on any NFT market or peer-to-peer. You're not locked in to any platform and you don't need anyone to intermediate.

The creator of an NFT gets to decide the scarcity of their asset.

A NFT item in one game can be transferred to another that's built on top of ethereum. It's also possible to have NFT-backed loans and fractional ownership.
All Ethereum products share the same "backend". Put another way, all Ethereum products can easily understand each other – this makes NFTs portable across products. You can buy an NFT on one product and sell it on another easily. As a creator you can list your NFTs on multiple products at the same time – every product will have the most up-to-date ownership information.
A lot of mining uses renewable energy sources or untapped energy in remote locations.
Ethereum is currently going through a series of upgrades, known as Eth2, that will replace mining with staking. This will remove computing power as a security mechanism, and reduce Ethereum's carbon footprint by ~99.98%1. In this world, stakers commit funds instead of computing power to secure the network.