It's pretty simple.
There are two bolts on both tranny and diff. One is a bolt plugging up the FILL hole (higher), the other bolt plugs up the DRAIN opening.
Whatever you do, first unbolt the FILL plug, because if that one is stuck or somethign and you already drained it, you're fucked.
If that plug comes off alright, drain it, then tighten the DRAIN plug, and proceed to fill it up.
Use long hose, funnel (placed at the side window height), and gravity-feed oil to fill it up, until you can feel the fluid level with your finger thru the FILL opening, or until it starts to drip out of the FILL hole.
Hope this helps.