On the top of the description area there are tow rows of icons. At the end of the first row is this icon <>. Click on it and an html box will open. Add your description in html format and on the lower right hand side click "ok". The description will show up.
In the left column under "Selling" click "Sold Items" you will see the list of items you've sold. Beneath the auction name and number you'll click on the link to "Send Invoice". or you can message the buyer for other methods of payment. Then, once you receive payment change the status to paid in the box at the end of the row. You may also show there that the item was shipped.