Offsets ... ?

[pidj]

Hi I have a 986 S with 18" wheels and I'm at a loss trying to understand wheel offsets, etc. All I want to do is push the wheels out so the tire edge is closer in line with the fender and the car looks more aggressive in stance. I don't want to compromise the handling or the wear and safety of it's original engineering. How do you determine what is used ( a spacer?) and how much and how does the offset play into that?

Thanks!