Don't freak out because of all the codes you see when you look at your position on the Y chromosome tree.
You do not need to learn what all of them mean. But you may be interested to learn the ones pertaining to your male line ancestors.
So please read a few more paragraphs for the sake of the legacy of your forefathers. And their potential contribution to haplogroup research.
The codes are the single letter names of haplogroups along with names of mutations.
These mutations must be named something. So a system of letters and numbers is used. The letter means who registered the mutation.
Of course you won't know what any of these codes are if you never saw them before. You can google them to see what you find.
Generally the higher up the tree you go (further back in time), the more likely you are to find research groups or documentation on origin theories. This is simply because the further back you go, the more common ancestors any branch has, and the likelier it is that there was at least one person (like me) theorizing about the origins of their lineage.
All men who are positive for some haplogroup descend from a common male line ancestor who lived some estimated number of years ago.
If you were using Clade Finder, click the to get to your branch on the YFull tree. It will show this information along with the flags of countries where men of this lineage trace their male line descent.
Click the to see your theoretical migration and relevant forums/groups in PhyloGeographer, a data-driven project that calculates approximate male line migrations from YFull and other ancient samples.
Why are there two naming systems - R1b1a2 and R-M269?
The original naming convention, and still used by ISOGG, is to alternate letters with numbers when new branches are found.
R1b1a2a2a4c for example.
The names eventually became too long for anyone to remember so most people use a new convention:
First letter(s) of haplogroup + name of one of the mutations defining the branch
You can think of it as defining a lineage by a chapter and page number.
The haplogroup prefix is the chapter of the book - in this case a major branch of "Adam".
The mutation name is then a page within this chapter - the particular child lineage of that branch
Why is this system useful?
In some cases it's necessary to define a branch by its haplogroup prefix and mutation because the same mutation may have occurred in multiple haplogroups. Though this is rare and usually indicative of an unstable SNP which should perhaps not be used for genealogy.
It is also useful to use the haplogroup prefix so that everyone instantly has some frame of reference for which major haplogroup the lineage belongs. Then they can decide if learning more about the lineage is worthwhile for their research.