What do delegate and undelegate mean?

Delegating means assigning your CHZ tokens, and subsequently your voting power to one or multiple validators to participate in securing the network by staking and in turn, earning rewards. When you delegate, you are not transferring ownership of your tokens but rather supporting the validator in securing the network.

Undelegating is the process of removing your staked CHZ from a validator. There is a 2 full epochs (roughly 2-3 days) waiting period when undelegating CHZ before you can claim them back. The Claim action is not automated and needs to be triggered by the user.