HI , I am new to this forum, I really need you guys to help me out. when i recieved the rims. it comes four black circle things. are those the offset (since i dont really know what offset is ) and when i install the rims. i just put those black circle things on the back of the rims. coz i didnt know which one is for the front and rear.

 

I think those are the hub centering rings. Aftermarket wheels will usually require these as they are usually not hubcentric. The hub centering rings will assure that your wheels are centered properly on the hub. They just pop onto the back of the wheel.