Hi pure!
Be warned, I don't use Microwatt, so if I'm wrong, I hope someone will correct me.
If I understand correctly, feh controls the wallpaper in Microwatt. I've never used feh before, so I'm not sure how it works. You could try this...
Press the Mod Key (Windows Key on your keyboard) + g
That is supposed to open up a Run dialog I believe. If it does, type feh in it and hit Enter. Perhaps that "might" open feh so you can mess around with the wallpapers.
To exit/close an application press...
Mod key + Shift + Q
Another helpful thing is to open your terminal, and enter...
h
then hit Enter on your keyboard. The h is for "help". That "should" bring up a list of helpful commands to use on your keyboard.
Hope that helps!
This is making me want to try Microwatt!