Lightning Pool allows you to buy and sell Liquidity. Someone who needs incoming liquidity would enter a bid order. Someone offering liquidity enters a ask order.
Introduction here: https://lightning.engineering/posts/2020-11-02-lightning-pool/ . Whitepaper: https://lightning.engineering/lightning-pool-whitepaper.pdf
An account is needed to work with Pool. It's an onchain transaction. Type pool accounts new to see how that works. After creating one, wait for the confirmation, then you can place orders.
If you want to offer liquidity (from your account balance) you do pool orders submit ask. Replace ask by buy if you want to buy liquidity.