A power down converts your STEEM Power to STEEM in equal amounts over 13 weeks. Each week 1/13th of your STEEM Power will be converted to STEEM.

The STEEM in your account can then be traded on an exchange.

You can stop your Power Down at any time.

"Powering Up" is when you add STEEM Power to your account.

STEEM Power is the weight behind your vote. It is good to have STEEM Power when voting on blog posts and comments. The total power of your vote is a combination of your Voting Power and your STEEM Power.

I posted information about a tool to monitor your voting power at https://steemit.com/steemit/@etcmike/steemit-tools-one-of-my-favorite-tools-is-steemdb

Steem on,
Mike