I wanna buy on-chain coins on ETH, but too expensive fee. Can L2 be used for this? I don't understand exactly how L2 works or how it can be used in this case.

Swapping $ETH for, say, $BANANA costs a lot of USD, esp if I only wanna buy a 100usd worth of $BANANA.

They say L2s are a way to transact with lower fees, but I don't understand how to use them or which one to use in order to be able to do a swap of ETH to BANANA, or is the use case of L2 different? I just don't get it. Do I first send ETH L1 to an L2 wallet or something and do a swap there?