ancestry does not give you the choice of being in or not. You are automatically in.
Not exactly. Ancestry allows you to opt in to seeing and showing matches or not. That is, if all you are interested in is ethnic/heritage information you can see only those results. You will not see whose DNA you match and your matches will not see that you share DNA with them. You can change this setting in future if you want.
tmm99 - If you have opted in to DNA matches. You get a list of people who have tested whose DNA you share with. For example, I have thousands of matchs (most are distant of course). You will see the name that that person has chosen to display on Ancestry. Some people use a screen name (much like here) while other use their real name as their screen name.
You don't get an email address for the person but can contact them through the ancestry message system (unless the person has opted out of messaging). People can "attach" their DNA results to their family tree if they want. Many people don't do that. People interested in genealogy do that. My husband knows his family but did DNA testing to try to help with genealogy. So he might see John Doe in his matches. If John Doe has a tree and my husband has a tree and they have a common ancestor ancestry will show that (that is will, tell him that he and John Doe are 4th cousins and will name the most recent common ancestors from their trees).
With adoptees, we often don't have a tree. So we are looking for patterns of matches. When I found my birthfather I had some information from him from my birthmother. I knew his first name and had a partial last name (spelling was not correct). I knew where he worked when I was conceived and knew that he worked for an oil company and was close in age to my birthmother. I had very little else.
I was able to rule out matches who matched my birthmother and focused on those that weren't related to her (therefore being paternal matches). My closest paternal matches were in the third cousin range. However, a number of them clustered around descending from a particular couple. I looked at the trees of some of those matches. Within hours I was able to trace down the trees and found someone of the right first name, consistent last name (matched the partial info I had) and right age. I found that the City directory for the town where my birthmother lived at the time and this man was in it working for an oil company.
I then continued to research him on Ancestry and found his college year book photo which I sent to my birthmother who quickly confirmed his identify. He was unfortunately long since deceased. Oh -- one cool thing was that I found out that he later attended law school and graduated from the same law school that I, many years later, also graduated from!
But, the point is that even from third cousin and more distance matches I was able to identify him. It helped to have the information from my birthmother but even without that I would have been able to narrow down to him, albeit a bit more slowly.
