Open up your Daedalus wallet

Go to Stake pool and delegation menu and click on Stake pools tab

Put the ticker of the pool you want to delegate to or simply choose it from the list

Click "Delegate to this pool", then "Continue" and select wallet you want to delegate from

Make sure you are going to delegate to the pool of your choice, click "Continue",then enter your spending password and click "Continue"

Voilà! You are now delegating your stake and you should see the rewards coming after next 4 epochs!

Delegation in Daedalus