Help with rear end gearing please.

Hello, I am still learning so forgive me, but I have been reading almost every book ever made for Mopar vehicles, decided on every part for my car from brakes, suspension, rear end, trans and motor.

But now it is time to get into depth with somethings like my rear end gearing. Can't truthfuly get my head around gearing, which one is best for what? etc etc. I was told 4.10s would be great for my car, but it was from my brother who runs high horsepower import cars, so not sure if that is good for my mopar.

Anybody able to PM or just plain post on here a quick learning guide of what I need to know to figure out best gearing would be of great help to me, thank you so much. Also, if you need info about my car and whatnot I will post that too, just not sure what is needed.