Every wheel has a centerline. This is 0 offset.What do you mean by a positive offset can you give me example please.
You can buy wheels with positive offsets or negative offsets. A negative offset will push the wheel itself out. This gives you more tire outside the fender. A positive offset wheel pulls the wheel in. The factory wheels have high positive offset (+44.45mm) in order to meet crash test requirements, fuel economy requirements, etc. and to prevent debris from flying out of the tires and damaging other motorists' vehicles.
Most guys stick with positive offset for these reasons, but go with less offset. Maybe a +10mm like I did, or a +18 or +25. Something along those lines. That way you're still pushing the tire out farther than stock, but you're not going nuts with it.
Some states like PA have strict laws regarding how your tread fits inside your fenders so everyone should be familiar with local laws.