Hi, Roxanne,
Stabilizer is a thin, non-woven material that most usually is made by Sulky. It can have a sticky side or not. There are several kinds such as tear-away or wash-away and several different weights. I don't normally use stabilizer for applique, but if you feel more comfortable using it, by all means use it.
Don't worry about being "green" or behind. This project isn't supposed to start until June 5, but we have quite a few ladies who have formed the "Jump the Gun" Club. :-) That's OK. I will be working right along with all of you once the sew-along begins.
Many participants will be contributing their vast knowledge of applique techniques as we work through this quilt. I would like to be working on AOTH, too, but I have a very full plate right now & need to get the commitments out of the way. Then I can settle down and concentrate on the Affair. For now, however, I have to be content with stroking my batiks.