Native staking is a way to earn passive rewards in SUI by helping to secure the network. From the Earn menu, you can select Staking to delegate your SUI to a validator and earn a portion of the network rewards. Note that native staking has a 24-hour "unbonding" period, meaning it takes one full epoch for your SUI to become available after you choose to unstake.
From the Earn menu, select Staking, then Earn by Native Staking, and choose a validator to begin.