Why networks pay you
Proof-of-stake blockchains are secured by validators who lock coins as collateral. Rewards compensate stakers for securing the network and for keeping coins locked.
Lock periods and APY
My Chain staking pools show an APY and a fixed lock period for each asset. During the lock you can't withdraw the staked amount; rewards are calculated on the published rate.
Judging a rate
Very high advertised yields usually carry higher risk. The coin's own price can move more than the reward earns, so think in terms of the asset first and the yield second.