Delegators participate in validation without hosting a full node. But by staking with validators, they can earn rewards and strengthen the network by paying a small commission fee (depends on the individual validator) to a validator of their choice.
This is for the people who are holding Matic tokens but do not wish to run a validator node. They have an option to stake their tokens with any validator of their choice after verifying a validator's performance and the commission charged. This needs to be done via a transaction on the Ethereum staking contracts.
The tokens get bonded with the next checkpoint being committed on the main-chain. Delegators also have an option to opt out of the system whenever they want and similar to validators, they will also have to wait for the unbonding period to end before withdrawing their stake.
Delegators also have an option to re-delegate their tokens with another validator. Rewards are accumulated at every checkpoint.