[surferfletch]

Start by searching "transmission fluid" and/or "transmission" to get all the answers to your 4L30-E questions. Here's the quick summary:

Drain and fill plugs are both on the tranny pan, with the fill plug toward the rear and higher on the pan.

You can drain about 4 qts. from the approximately 9 qt. system. You refill with the engine idling in neutral. You should run it through the gears a couple of times as you top it off. You'll need a cheap hand pump to get the fluid up in there. Fluid exchange is an option. I drain and refill a couple times every 15K and I drop the pan and change the filter and gasket every 30 K. 155K and the tranny works great!

Good luck!