Here's Instruction How to Install of Bushwacker Fender Flares:
2. Apply the double sided tape that came with the fender flares to the inside edges of the flares. The tape length should fit exactly with the fender flares. Smooth the tape so that it adheres well to the flares with no wrinkles or bumps. Pull the plastic off the exposed side of the tape and place it on the very edge of the fender, just above the wheels. The flares are made to fit and follow a variety of vehicle shapes and body lines. Press the flare against the fender to make sure it is fully attached.
3. Place the new bolts for the Bushwacker flares through the holes where the previous fender flares were on your vehicle. If you had no existing fender flares, use the self-tapping screws that came with the Bushwacker flares. Place them in the holes through the flares, and screw them through the metal fender with a drill. No nuts are needed on the backside of self-tapping screws.
Note:If you want to paint your Bushwacker fender flares to match your vehicle, it's best to paint them before installing them.
Source: How to Install Bushwacker Fender Flares