I got the big wood letter at Hobby Lobby for $12 bucks.
I bought the moss at Hobby Lobby for $10. It comes on a roll or in loose pieces in a bag. I bought the roll which makes it really easy.
Lay down the letter upside down on the sheet of moss, and cut with a razor blade around it, leaving about an inch extra all around.
I lifted the letter off the moss, and sprayed the front with spray mount glue.
put it back down and press hard. Then, I cut around the edges to start wrapping it around the back and gluing it with my glue gun.
Here is a picture of it wrapped all the way around the back. And that's it! I added a strip of burlap I cut to hang it on a wreath hanger, and voila!