hey guys
need some help with soem technical info again

ok
im looking at some rims for my ek4
and im set on getting a set of 15 inch gram lights 57S

now what i dont understand is the offset
ive done soem reading online but still dont quite get teh concept
so can someone put it in dummy terms for me?

ek4 stock rims are 15x6+ 45
the gram lights 15 inches are 15x6.5 +38

what exactly does that mean and what effect is it gonna have on my car

thanx guys