I understand "animate" vs "inanimate". However, I do not understand what "not personal" means in this respect. That is my first question. Second question: does statement above tell me that singular pies is "personal" and plural psy is "not personal"? If yes, why would singular vs plural change that in a noun?
those are two different things. techniacally pies is animated not-personal.
a noun being animated or not is important for singular, if a noun is personal or not is important for plural.
Basically masculine nouns are divided into three categories: Masculine personal (mężczyzna, chłopiec, ojciec), masculine animated not personal (pies, kot,), masculine not animated ( zeszyt, stół, chleb).
Personal nouns describe people. not personal nouns describe everything else.
Masculine personal nouns , are masculine nouns that describe people,
not masculine personal nouns are either masculine nouns that do not describe people, or all feminine and neuter nouns.
OK, I just have to say this. As far as languages that decline nouns go, over the years I have studied Latin, Russian, and Ukrainian so far. (German hardly counts, because its declension system is so simple by comparison.) But I have never yet seen a language as complicated in its nominal declensions as Polish. 'Masculine animated not personal' ... it's almost too much to believe. :-)
However, I'm also very thankful that I have that experience. When I see people in these early stages of the Polish course asking "what do nominative and accusative mean?" I feel very sorry for them. They are really in for a tough road ahead. I can't even imagine trying to tackle Polish without having any prior experience in studying a language with complicated nominal gender and case systems!