Conversation so far:
when does leo come out as a whitelighter
Leo comes out as Whitelighter in the Charmed  episode Blinded by the Whitelighter.
what is a whitelighter
A whitelighter is a guardian angel and mentor in all things magical
what did leo do as a whitelighter in Charmed
Leo was a guardian angel to the three sisters as they grew in their power.

Question: what was the guardian angel's powers
Self-contained rewrite: what were leo's powers as a whitelighter