Delegation allows you to earn rewards for delegating some stake without the need to run a node or become a baker. For more information about delegation, see Delegation.
Before delegating any of your stake to a baker or pool, use the CCD scan tool to research baker pools thoroughly.
You can only have one delegation per account. If you wish to delegate stake to multiple open pools, you can have multiple accounts and transfer CCD to those accounts to delegate.
An account cannot be both a baker account and have a delegation.
The Delegation FAQ answers many commonly asked questions.