Activating

What does it mean for the state of my stake account to be activating?

An "activating" stake account means that you have selected a validator to delegate to and the stake account will become active at the start of the next epoch. Your stake account is waiting for the epoch to end to become active. At this point there's nothing else you need to do, however, if you want to change the validator you delegated to, you can click "Re-delegate".