There's a fast-motion video in the description if you're interested. You might get more of an idea from that. But I use a woodburning pen with some different tips (like this: goo.gl/nM0JX1 ) and those heat up enough to burn the surface of the wood enough to make something out of. That's pretty much woodburning summed up.
Thank you! I have a Detail Master brand pen. I used a small pointed shader tip for the person, around the person, lettering on the fence, and the horse's face. A medium shader for the rest of the horse. A arrow type shader with sharp edges for the tail/mane. And a large shader for the foreground and most of the fence.