great, the offset is the distance from the centerline of the rim to the wheels mount pad, the area that attaches to the hub.. this is in millimeters, a positive=outside the centerline-outside is of course the wheel front(part thats looks good)like, 45+ means that its 45 millimeters from the center of the wheel towards the front.. the bigger the number the more the rim sets in the fender. the smaller the number and the negitive numbers will push the wheel out of the fenders giving you that wide mean look, but go to much and your wheels will rub in the fenders while turning and even the top of the fender if you lower the car.. most people add lots camber to help clearance issues..but rim width will also change the offset you need to clear everything while turning.. no worrys for most though cause you got room in the fenders an can chage sizes and offsets here and ther and still be fine..if you have more questions let me know, thers more to it, but it takes time to type, ill be glad to help if needed..