Its with you sat in the car; the front is the bit forward of the steering wheel, where the engine is found and the rear is behind you.... That is as long as you are still facing forward looking to the front!!
and, as long as the car is right hand drive, ie made for UK roads,
The front left of the car is the area with a seat but without a steering wheel and the front right is the area of the car with a steering wheel...
It's a reasonable question asked by the OP. It may seem simple but it could just as easily be the side of the car viewed from the front and not the back.Evrythings easy when you know the answer.
For clarification , The left side is the passenger side.