The plugs prolly take a T55 or 1" wrench to undo, the lower one is the drain, take it out and all the oil pours out....
The one tahts about 1/3 of the way up and is the same type of plug is the fill hole. Fill it up till the fluid flows back out the upper hole, then its good and full.
I like to put a tip on the fluid bottle with a hose - put hose in hole, squeeze bottle to fill. Makes less mess, its tought to get in there to fill it up. Will hold about 2 quarts.
You can buy the expensive blue oil from the dealer, or use ATF, whichever you choose.
2007 Silverado LT Z71-
Pantom Grey, 5.3L, loaded, CAI, HID projectors, LED exterior, AirAid, tinted 15% over factory, color matched and debadged, 20" Platinum Boulevard wheels, ProComp 2", RollPan, custom duals, RST spoiler
1993 S10 Blazer Tahoe LT-
Green/Grey, 4.3 Vortec (W), 4x4, loaded, LT265/70R17 (33"), jacked 3+3, ALPINE and JL system 880watts, K&N, 6000k HID, complete LED upgrade, lots of new stuff. Slowly modding and restoring - got a build thread