YumiSwap is an Automated Market Maker (AMM), and the Exchange is at the keystone of YumiSwap.
YumiSwap lets users trade without the need to go through a Centralized Exchange like Binance. Everything you trade on YumiSwap is routed directly through your own wallet.
The YumiSwap exchange can only operate when there's enough liquidity to support trades; if nobody wanted to sell you CRO for example, then it wouldn't matter how much you wanted to trade for some.
Providing liquidity will get you LP Tokens and it will earn you rewards in the form of trading fees for making sure there's always liquidity for the exchange to use.