Offset is measured in milimeters not letters. Offset is where the backside of the mounting pad is located on the wheel from center. Back spacing is the measurement from the back of the mounting pad to the back side of the wheel. Typically speaking, the higher the offset, the more the wheel will tuck inwards towards the suspension. The lower the offset, the more the wheel will push out towards the fender.

For Example:
If you have a -12mm offset on a 9" wide wheel, the mounting pad would be 12mm towards the
back of the wheel from the center. If you have a +12mm offset on a 9" wide wheel, the mounting pad will be 12mm
forward from center.
All the wheels linked in post #2 are guaranteed to fit your vehicle stock

If you want some additional attention with your package, give us a call at at 1.888.459.4080 and anyone of our sales agents would be happy to help.
-Matt