I had a Colorado some while back and if I recall it had a sort of wire / stick affair that went down the side of the engine under the bonnet. I don't quite know how it worked, but there were some marks on it that showed the amount of oil in the engine. I think that you had to do it when the engine was cold. But if you pull it out, there should be a sort of black liquid on the end of the pole. If it was between the marks, it was good. Mine was right at the bottom, so I put some oil in and then it was fine. The light went out too. Which was a relief.
Hope this helps. I didn't keep the manual, I sold it with the car. Wish I could be more help! Let us know how you go on.
Best wishes
Chris