The exchange is where you can trade one token for another. It is a simple swap interface, just select the two tokens you wish to exchange.
The liquidity provided to the exchange comes from Liquidity Providers ("LPs") who stake their tokens in "Pools". In exchange, they get LP (Liquidity Provider) tokens, which can also be staked to earn MID tokens in a "farm".
When you make a token swap (trade) on the exchange you will have to pay a 0.2% trading fee.