Hi Nikki, thanks for your post on G2G. You should be able to add your Gedmatch ID # to your DNA test page on your profile. Go to your profile and highlight the 'add' link near the top right. Then click on DNA Test Information. The first thing shown on the page is 'Ancestry DNA'. Look towards the right of that line and you'll see a button that says 'Edit or Enter More Details'. Click on that, and a page will come up that has a place for your Ancestry.com user name and another box/place for your Gedmatch ID. Enter it there and then be sure to click on the 'Save Details' button towards the right of the screen.
As far as Ancestry and DNA Circles, you cannot use those to confirm ancestors. They do not in fact confirm ancestors. They are clues to shared ancestors. So you can't confirm ancestors solely based on others showing up in your ancestry.com DNA circles. If you've uploaded to Gedmatch, you can look for triangulated groups (where you share a common segment on a chromosome with two or more other people) and if you all share a common ancestor (as long as the other people you're matching aren't close relatives, i.e. parent/child, siblings, aunt/uncle & niece/nephew), then you can confirm a common ancestral couple.
Since you're new to DNA and having problems understanding the explanations, I'd suggest you spend some time reading about autosomal DNA and what you can do with your results. I highly recommend the ISOGG site. You might start at this page and then click on various links and read the articles and/or watch videos: http://www.isogg.org/wiki/Beginners%27_guides_to_genetic_genealogy
