Could someone please tell me the difference between the core rules and that of a normal BGII game. Thanx appreciate it.

Huh? Regular baldur gate rules are the core rules. Setting 3. You can adjust the rules up or down in difficulty depending on what you want.

There are 5 levels of difficulty. Level 3 is the basic core rules in BG2.

I'm not an AD&D player, but from what I know the only difference between normal & core rules is that under normal rules, spells are always memorised successfully (under core rules, there is a chance of failure); and you get max HPs when you level up (core rules - you get to "roll" a die).
I suppose normal rules allows a player to avoid reloading to get the best possible stats.