At the moment if you try to leave them as default it doesn't keep the strings, so for now you'll have to fill them all out (I have fixed this in the next version though!)
The stats dictate how much damage you do in battle mainly (although there're a few instances where they change how you can interact with things ;) ). Good to know you find the affinity stuff a bit vague tho, I'll have to have a think about that for the next release