Wheel backspace questions for a 3/4 ton

[Mmorgan32]

I'm looking to get new wheels for my truck my truck has stock 16s which I'm assuming is 6in wide. I know nothing about backspacing all I know is I keep seeing 8 lug wheel with a -12 or 12 or 0 backspacing. I hate how far in my wheels sit so I want to get a 16x8 my tires are 235-85-r16. My question is what's the difference in the backspacing, what would bring my wheel out flush with my fender or stick out just a bit and what would work with my tires?

I know I could just go to a tire shop and ask but it's 8:30pm where I live and I wanted to see if I could get an answer soon than tomorrow morning lol