Thank you, glad you like it.

About your question.
If you have Steem on another platform you first withdraw it to your Steem account here.

When it has arrived in your wallet you click on the dropdown menu behind the amount of Steem.

There is a menu item called Power Up. When you select that you can decide how much Steem you want to power up.

Then you need to confirm it with your password and its done.

Hope this was of help to you.