Thanks for the site Cap.
What if you don't do any ecthing...just a color stain. Also, I have glue residue from outdoor carpet.
If you are just wanting to stain some concrete, than that will be considerably less costly. I can't tell you how to get residue from the outdoor carpet up, but once you do, you will probably want to have it powerwashed or some other method to get everything off the concrete.
We get our stains from a company that sells costruction materials and they can come in either a powder or liquid form. Not sure if you can get this kind of stuff at a Lowes or HD. You can either roll it on w/ a paint roller or spray it on w/ a garden sprayer depending on the look you want. We put different shades in the release agents when doing new patios to give some variation in color. Truthfully, I have never done staining on existing concrete, but am pretty sure its not a big deal. I just googled "concrete stain", and this site was first on the list and seems to have a lot of good info.
http://www.concretenetwork.com/stained-concrete/