Understanding Ellipsis Pools
Ellipsis Finance is an Automated Market Maker (AMM) or exchange that lets users and other decentralized protocols exchange tokens (BUSD to USDC, for example) with low fees and low slippage. Unlike exchanges that match a buyer and a seller, Ellipsis uses liquidity pools. Let's review some terminology before going into more details.

Terminology

Liquidity pool: a smart contract that holds tokens deposited by liquidity providers. When a swap is made on Ellipsis, it will use these tokens to fulfill the swap.
Liquidity provider (LP): any user that provides liquidity (tokens) in a liquidity pool.
LP Tokens: tokens that an LP receives for depositing liquidity (tokens) into a liquidity pool. These tokens represent your share of the liquidity pool.
Liquidity Incentives: Ellipsis offers EPX rewards on most pools, and some pools have extra rewards available. These rewards are given to incentivize people to deposit their tokens to Ellipsis. On Ellipsis, liquidity providers must stake their LP tokens in order to receive these rewards.
A liquidity provider deposits their tokens into a liquidity pool and in return they receive LP tokens. Then these LP tokens can be staked to receive LP incentives.
When they want to leave the pool, liquidity providers must unstake their LP tokens, and then exchange the LP tokens for the tokens in the pool.
For example an LP can deposit BUSD + USDC into the 3EPS pool and will receive 3EPS LP tokens in return. When they want to leave the pool, they return the 3EPS LP tokens in exchange for BUSD + USDC.

Using Ellipsis Pools

Choosing a pool

Ellipsis has pools for a wide variety of tokens. When you provide liquidity to a pool, no matter what coin you deposit, you gain exposure to all the coins in the pool which means you want to find a pool with coins you are comfortable holding.

Does the coin you deposit matter?

Apart from the deposit bonus explained below, it doesn’t matter. Your tokens will get split into the pool and it doesn’t affect your returns; so you can deposit one, some or all the coins into the pool without worrying about it affecting your returns.

Understanding deposit bonuses

On the screenshot above, you can see that USDC and BUSD are lower in the pool; so if your plan was to join the this pool, you would ideally deposit USDC or BUSD into it. As you can see on the screenshot below, you would get an instant 0.0571% bonus for depositing BUSD into the pool.
The main reason for this is that BUSD-T are is slightly less expensive at this moment. The deposit bonus reflects that.
The pools are always trying to balance themselves and go back to equal parts, so depositing the coin(s) with the lowest share will get you a deposit bonus.