Something Ive always wanted to know since at home we have a tropical tank with a couple fish. How do you tell if 2 fish are attacking eachother? Is chasing/nudging part of fighting or just normal interaction?

Chasing/nudging is pretty normal. Goldfish regularly compete with each other for food or for play. HOWEVER, if at any time you see that the behavior is stressing your fish out or causing physical damage, that's when you need to put your foot down and consider separating them.

I noticed when I had bits that even when kibbles nudged or what may have bit biting? bits he swam away at first, but for the msot part they liked to be around eachother. Theyd stay near eachother usually in teh same half of the tank and stuff. Is that a good sign tha tmaybe kibbles wasnt a vicious nasty?

Probably, if one didn't like the other then in theory they would stay away from each other. So Bits must be able to tolerate Kibbles with no problems. Theoretically speaking.

I once had one fish chasing & nudging ALOT . I finally separated them when I noticed the "chasee" getting exausted.