Okay, so I am dating myself a little, parodying "you've got mail" but I think it's the closest thing I could think of to describe the excitement (which we all had initially with AOL), of receiving my first autosomal DNA matches on my parents and my DNA.
Then I tried to figure out the matches. Oh, my. Out of the 2000 matches for my parents, I have figured out 13 easily. The rest has had me scratching my head. I also signed up for gedmatch, a free site run by donations (hint if you use it, donate), which is currently down while they upgrade their servers. I got several more matches (about 1400 per person), but had some bumps along the way as I learned just how to navigate triangulation of matches.
The first thing I learned is just because two people match you at the same point on the same chromosome, doesn't mean they match each other. You get half of that DNA from each parent, so if they don't match that means that one person matches DNA from your father and the other your mother.
The second thing I learned is that sometimes large segments get passed entirely from parent to child. What that means is that if my Dad has a 28 cm match and I got it, the relationship estimate for my relationship won't be accurate. I don't think this is so much in the matches for 1-3rd cousins but beyond, it can make it harder to locate the relationship. Mom has a 6th cousin she shares a pretty large segment with, that I don't match at all, but she has two 4th cousins from the same line that I match in the exact way.
The third thing I learned was how to use some nifty free tools available. For 23andme.com, you can use DNAgedcom to download a zip file with specific data. You can also install the 529 extension in chrome. Genome Mate a free program is a desktop database/spreadsheet program that allows you to track your matches across several venues (gedmatch, 23andme, ancestry.com, ftdna, etc). All these tools are going to be needed, unless you can do it yourself, because you must keep track of the matches.
If you don't have surnames in common, you need to cross your fingers for some more matches in that segment. Chances are even if you have a fairly robust tree, you don't have adequate research on the cousins of your 4th great grandparent. Or you haven't researched all the lines from each sibling of that great grandparent. Some folks have a tree, but some don't. It is somewhat frustrating because I thought DNA would make it easier to break down my brick walls. So far, it's given me a lot of information that I have no clue how to use.
When you have a match, it is helpful, because anyone in that segment who matches your match shares the same common ancestor. Because a rather large group of my McCurdy cousins have tested, I was able to work with them and we have started compiling a list of specific segments that are "McCurdy" but here's the best part, we don't all match each other in the same place!
Because of intermarriage of cousins and more, we have a rather complicated tree on my McCurdy's.
Cousin A has two great grandmother's who are sisters, and daughters of my Dad's GGGrandfather's brother.
Cousin B shares my Dad's GGGrandfather, but is only a half sibling descendant. The other half on that same line is a niece of Cousin A's McCurdy's (and, lol, she shares the other Surname Morris).
Cousin C shares my Dad's GGGrandfather and GGGrandmother.
Cousin D shares only a 3rd G Grandfather of my Dad's with the rest.
Cousin E is a half sibling descendant of the 3rd GGrandfather, but we found out that Cousin B and Dad match her mother who isn't a McCurdy (she matches none of us on the McCurdy's).
Only one match is in common for more than two of us. Another match may in fact be a match to the Beck family (the wife of Dad's GGGrandfather) and not a McCurdy Match. We have several more cousins awaiting results, with each piece we will build it together. We are hoping we can get Cousin B's mom to test because she and her first cousins that are alive are the closest we can get to Elijah McCurdy (great grandchild) and we are hoping it will open up other McCurdy families.
As you can see, it's complicated. It's not easy, but it sure is fun.
Will keep you posted.