Step 1: Go to https://www.eggs.cool/ex/#/pool
Click the large "Add Liquidity" button
Step 2: Select which token pair you want to add liquidity for:
Fill in the amounts you want to add to the liquidity pool. It may ask you to "Approve" the tokens - you will have to send these "approve transactions" first. Once you've approved the token you can hit "Supply"
Then a transaction will pop-up for you to sign in your wallet (like MetaMask) - after the transaction is complete you will have successfully added liquidity.
The transaction will provide you with some "SLP" tokens in your wallet. These are Eggswap LP tokens and represent the share you've deposited in the pool. All pools are labeled as ELP but represent different pools.