Well, it's quite a lenghthy process, especially if you're not fluent with things like this, but here it is anyway:
I used Photoshop. Create your avatar (I had to use 2 different ones for cutting and pasting to get the desired position) and get the zoom the way you want it and everything. You can also mess with different buttons to make the avatar make different faces. Then push the "Print Scrn Sys Rq" button on your keyboard (usually right next to F12 on the right). This will take a picture of the entire screen. If you have Photoshop and you can use it fairly well, then it's your best bet, but if not paint SHOULD do the trick, but no promises. Go to whatever program you're going to use, open a new project (if necissary), and paste the picture into the new project. Then, select the recangular marquee tool and make a rectangle around the avatar box, cut it, open another new project and paste it there.
Now you have the picture in whatever program you want to edit it with. I can't really go into detail after that because it just depends on what you want to do with the picture. You can cut certain parts off and rearrange them, or you can bring in other pictures with people in different positions, cut from them, and paste them to the picture to create new looks. Sometimes it works, sometimes it doesn't.
This is the same concept I used for my Krystal Pic: I found several different poses and put them all together and changed them around to form the pose that I wanted.
You can see that pic
here
Anyway, best of luck!