Think of it like this... private means password..
Posting key - your social media.
Active key - you are your own bank, this is for the safe / vault access.
Owner key - you will need this stored in an offline or otherwise "safe" place and only used in emergency to recover or change your other keys. If an app asks for owner, use active if, and only if, you are comfortably confident with their service bringing benefit to your steem account.

As for the public keys and such listed on your wallet permissions tab, ignore those, that's for developers and should be hidden by default.

It's really quite simple.

• steem
• keys
• private
• public
• thoughts
• partiko