Things you should know
Due to common trends people will often say "needs more offset bro" meaning the wheels should stick out more towards the cars gaurds....funny thing is in order to do that you want less offset.
To put it simply, offset is the distance, mesured in millimeters, from an imaginary centre line through your wheel to the hub mounting face of the wheel (where the wheel bolts to the car. If that point is closer to the front of the wheel (the face) then your offset is positive.
However if the mounting face is closer to the rear of the wheel the offset is negitive (low offset).
The higher the offset, the more it sits inside the gaurds of your car. Most modern cars are equipped to take a high offset with many factory wheels being around 40-55p (positive).
Older cars are more likely to have a lower offset.
PCD - Pitch Circle Diameter
|The PCD of a wheel is the diameter of an (imaginary) circle going through the centre of the holes in the mounting face of the wheel.
For example 5x114.3, where 5 indicates the number of holes and 114.3, a diameter of 114.3mm.
CBL Rings - Centre Bore Locating
Another thing people get confused with is CBL (centre bore locating) rings.
When possible quite simply use them, however in most instances you will never know if you dont have them.
The role of the CBL ring is to put the vehicles weight on the hub rather than the wheel studs.
On factory wheels these are not required as the wheels are made to fit the car and are allready "hubcentric" however when fitting aftermarket wheels they usually have a generic size hole in the wheel to allow fitment to multiple vehicles.
This is where and why the CBL ring is used.
If not used, in some instances it will cause your car to shake through the steering wheel which is often mistaken for out of balance wheels.
If they are there then use them, but if not, don't stress too much.