My friends and I have been playing DnD 5e for a few years now, but now I’ve decided to start GMing PathFinder 2e. We’ve played through most of the Beginner Box, and now I want to continue with my own homebrew content. As part of my world, I want to introduce a fighter “subclass” (probably the wrong terminology for PathFinder). What I want is a tribe of warriors who fight without armor (starting at level 2 or 3), and to compensate for the lower AC they get magical tattoos which increase their AC. It will also be possible (when you advance in levels) to choose to add other tattoos with other magical effects.
So my question is: Is this what archetypes are for? Because I don’t think “subclasses” are a thing in PathFinder? Or how would I go about this?
It's closer to the way D&D 4e did multiclassing. 5e-style multiclassing simply isn't possible in PF2.
But yeah, "multiclass archetypes" are the closest you can get in PF2 to multiclassing. Other non-multiclass archetypes exist too, and these are most similar to D&D 5e's "prestige classes", which exist only in the form of a single Unearthed Arcana (the "Rune Mage") and a few homebrews (Walrock Homebrew's "Vampire" prestige class was especially good). Basically: it's things where you get too many different abilities and have some kind of progression, so it's too much for a simple feat, spell, etc., but not enough for a full class, and probably not something you should be at level 1.