I usually use a drill bit called a step drill (cheap at Harbor Freight and adequate for this job). It allows a prgressively larger series of holes to be drilled through sheet metal until it makes one big enough. You just need a hole big enough for the base of the antenna. Fasten the retaining nut on the back of the mount. (You might have to remove a fender liner to get to it.) The coax cable (wire from the bottom of the antenna) will often squeeze through an existing hole in the firewall next to something else going through it. If not, just drill a hole, but make sure it doesn't go into the heater core, windshield wiper mechanism, or a blind cavity like the defroster tunnel. That usually means aiming kinda below the lower line of the dash board. Once the cable is inside, plug it into the back of the radio. Seal the firewall hole with foam, a grommet, or seam sealer. You can probably get some very specific instructions for your model for the price of a fast food meal. Just take one of the local audio dealer techs to lunch. They normally are very excited about their work and will talk extensively for free food, since most of them are not paid a lot.