A draft, in regards to emails, is a copy of your message. If you are in the process of writing and don't finish, or send it it, the app saves your work for you.
In gmail, under labels, you can select a draft message and go in and finish it off and send it.
Alternatively, you can look at your drafts in gmail, and put a check in the box for right one and then you should see an icon for the trashcan.