Any user who delegates their SOL to a Validator (either directly or via Stake Pool), enabling them to validate new blocks and keep the network alive, becomes a Delegator.
Anyone who has some SOL in their wallet may delegate it – and earn rewards by doing so.
What is a Staking Account?
It is a separate account where you place your SOL that you want to delegate, or stake to a validator (not to a stake pool). Follow the wallet's instructions to create one—or to withdraw your SOL from it back into your wallet. You can also use JPool's interface to deactivate a staking account or withdraw SOL from it.
What is a Stake Pool?
Here's what Solana Docs have to say on Stake Pools:
"This on-chain program pools together SOL to be staked by a manager, allowing SOL holders to stake and earn rewards without managing stakes. Users deposit SOL in exchange for SPL tokens (staking derivatives) that represent their ownership in the stake pool. The pool manager stakes deposited SOL according to their strategy, perhaps using a variant of an auto-delegation bot as described above. As stakes earn rewards, the pool and pool tokens grow proportionally in value. Finally, pool token holders can send SPL tokens back to the stake pool to redeem SOL, thereby participating in decentralization with much less work required."
To put it short:
You have all the advantages of direct staking at top efficiency – without the fuss of selecting and carefully watching the validator(s) you stake with.
Plus, you help improve the Solana network, which increases the value of your SOL!
What is a JSOL token?
When you delegate your SOL to a Stake Pool, you get JSOL tokens in return. These tokens are your proof of a share ownership in the stake pool, and they can be traded back for SOL at the end of any epoch.
Obviously, you get more SOL than you staked in the first place, including your APY accrued over the staking period.
How do I get my rewards?
Your JSOL represents your share in the pool’s total stake, which grows constantly as rewards are accrued.
This reflects in the JSOL-SOL exchange rate which will be used to calculate the SOL you get back when you unstake.
Total JSOL price growth is equal to the pool’s APY (slightly above 7% p.a.).
What is a Liquidity Pool?
Here's what Cryptopedia has to say on liquidity pools:
A liquidity pool is a crowdsourced pool of cryptocurrencies or tokens locked in a smart contract that is used to facilitate trades between the assets on a decentralized exchange (DEX). Instead of traditional markets of buyers and sellers, many decentralized finance (DeFi) platforms use automated market makers (AMMs), which allow digital assets to be traded in an automatic and permissionless manner through the use of liquidity pools.