Dear Steemit Friends I have some confusion about Potential payouts, can anyone help me to explain about it.

My post is showing potential payout 0.010 or 0.020 but when time complete I got nothing. Why there is no reward and how much potential payout is necessary for pay out.

Now I have 51 Steem Power, but after getting this Steem Power , my delegated Steem Power vanish.
I asked this question many time but no one is replying....