what does start power down steem mean?

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

Thank you Mike!

Congratulations @sarah72492! You have completed some achievement on Steemit and have been rewarded with new badge(s) :

Award for the number of upvotes

Click on any badge to view your own Board of Honnor on SteemitBoard.
For more information about SteemitBoard, click here

If you no longer want to receive notifications, reply to this comment with the word STOP

If you want to support the SteemitBoard project, your upvote for this notification is welcome!

Steem Power gives voting power, so the more SteemPower you have, the more value it has when you upvote or downvote things; however, SteemPower is non transferrable . So you won't be able to send it to someone else or sell it like you could Steem. You can Power Up to turn Steem into SteemPower (this is instantaneous), and you can Power Down to turn SteemPower back into Steem (but this takes a long time).
When you power down it'll take 2 years to get it all. Steemit pays 90% extra reward for steem power. If I am not wrong, for example if you have 100 steem in steem power you could get around 190 steem after a year. So basically, if you power down after a year then 190 would be divided by 104 weeks(2 years) and you will get the equal share every week. So you have to wait for 2 years to get back all 190 steem.
Hope this answers your questions :)

Congratulations @sarah72492! You have completed some achievement on Steemit and have been rewarded with new badge(s) :

Award for the number of upvotes

Click on any badge to view your own Board of Honnor on SteemitBoard.
For more information about SteemitBoard, click here

If you no longer want to receive notifications, reply to this comment with the word STOP

If you want to support the SteemitBoard project, your upvote for this notification is welcome!