The letter (or letter group) names the major branch of the paternal tree, and the code after the dash is the specific defining marker (an inherited mutation) that pins you to a sub-branch. So “R-M269” means branch R, defined down to the M269 marker. A longer, more specific code just means a deeper, more recent twig.
What do the letters and numbers in a haplogroup name mean, like R-M269?
What the branch letter and the marker code mean, and why a longer code just means a deeper twig.