Transfer case is easy, crawl under & find the big aluminium thing (T-case housing) that the front drive shaft is bolted to...on the back side (toward the rear tires) are two plugs, one high & one low. (almost to the bottom)
Remove the upper plug with a 3/8" ratchet & some oil should come out, if not, stick your little finger in there to see if you can touch the oil just below the hole.
If you have oil on your finger, you're pretty close to full, but it wouldn't hurt to top it off. (Dextron II ATF, IIRC)

Checking the trans. is a little more involved, but goes a little something like this...



Before you do any of the above, park on level ground.