Re: ?? how ??
Well, pull the fill plug. It's the giant plug that is right next to the speedometer cable. I don't know what size it is but a crescent wrench fits it just fine. haha.
Anyway, I fill mine with an oil squirt can. After about two quarts fatigue starts to set in though (especially when it's snowing outside). I have one of those nifty pumps that you can buy for $4 at an auto parts store that fits on a quart container but I've never used it. Yeah, I'm a little weird.
I almost forgot, fill it until it's within 1/2" of the bottom of the hole. Anywhere between just barely coming back out and 1/2" below is good. I think GM recommends 1/2" below for full time systems and to the bottom of the hole for part time systems. I might have those backwards now that I think about it..