If you like the offer, go to the bottom of the offer, make sure it says "accept" and click update. Then you'll see the traders name and address and you can also send a message if you choose to.
If you want to make a few changes to the offer, make sure it says "counter" and then you'll have the ability to add or subtract cards from either traders side. Once you have your counter offer ready you can click submit and send a message if you choose to.
If you just flat out don't want to deal with the trade or trader, make sure it says "decline" and submit. At that point you can also send a message explaining why you declined if you want to.
Hope this helps! Welcome to the database!!