Chevy surburban leaking oil from the rear

I believe you are talking about the rear differential. I would not drive the vehicle if you think there is a possibility that the fluid level may be too low.

Oftentimes a leak is only a bad cover seal. Your best bet is to crawl down there, place a wide tub you don't care about underneath to catch the fluid, and take off the rear cover. That's the best way to drain the fluid. It will come pouring out when you take it off. Inspect the differential case, the cover you removed and the gears for any damage.

Get a new seal for the cover, replace the cover, torque down the bolts and fill the differential with the proper amount of fluid. There should be a filler hole up near the top. If you have a limited slip differential, remember to get fluid rated for it. I hope this helps.