The key directories to look at are vaults, strats and harvester. The vault is where users deposit and withdraw their underlying and yield assets. Strats stands for strategies and they are the strategies the protocol uses to generate yields. For example, it is using Compound, Harvest, Yearn and YCredit as yield strategies. Harvester is the interface to harvest yields from the vaults and then swap them for yield assets (ETH, WBTC, YFI).