You'll only need a few supplies for this project: a base, a covering, and an adhesive. I decided to use a 20"X30" foam board for my base, since it was inexpensive and easy to find. I opted for the thickest one I could find to make it sturdier, but you could definitely use something thinner (or smaller) if you want to. To cover the board, you can use either felt or flannel (felt pieces will stick to either). I prefer to use flannel since it's a bit cheaper than large rolls of felt. I used 1 yard of gray flannel for mine. And, lastly, for glue I used some spray adhesive. But you could easily use Modge Podge or something similar instead.
Simply lay out your board and wrap it in the flannel, just like you would when wrapping a present. If it looks like you have too much flannel to work with, now is a great time to cut off any excess. Once you have your "wrapping plan" figured out, you can start applying your adhesive. If you're using spray adhesive or something else that dries quickly, I recommend doing this in small sections so that you can put it all together without feeling rushed. Be sure to pull the flannel taut as you go to avoid extra wrinkles.
If you've never played with a felt board before, all you really need to know is that pieces of felt (or flannel) will just stick to the board without any extra adhesive or velcro. They aren't permanently attached so you can easily move things around and change out your board whenever. Super cool. So the possibilities are basically endless! Since it's fall, here's one simple Halloween-themed idea to get you started: Jack-o'-lanterns.
Update: If you're looking for more ideas, you can check out the pizza and ice cream felt boards here.