Auxiliary lights work in conjunction with your standard headlights to give you improved visibility in different driving conditions. There are two basic types: driving lights and fog lights.
Driving lights work with your hi-beams for greater visibility at longer distances. They project a long, narrow beam of light in a variety of patterns which greatly extend your range of view. Fog lights work together with your low-beams to improve your visibility in foul weather, such as fog, rain, snow and mist. They emit a low, wide pattern of light that's designed to shine below the haze. This reduces the amount of blinding glare that occurs when you turn on your hi-beams in foggy weather.
Your auxiliary lights are controlled by an in-dash switch. During the installation, the wiring harness will have an extra cable that runs through your firewall (don't worry, there are pre-drilled holes for wires to pass through)
The difference between regular auxiliary lights and off-road auxiliary lights is that off-road lights are built to withstand harsher conditions. Think of the difference between a Cadillac El Dorado and a Jeep Rubicon. The Caddy is a solid set of wheels, but you would not want to race it in the Baja 500. The Rubicon, however, has a special suspension, 4-wheel drive capabilities and a roll cage, so it's ready to shred through any mud bog. Similarly, off-road lights are tougher, sealed tighter and are larger than regular auxiliary lights, making them better equipped to survive a wild trek across the badlands.
The installation times are different depending on whether you are mounting auxiliary lights or OEM replacement lights. Auxiliary lights, including the off-road variety, are easy to install, but they take a tad longer then the OEM lights. All you have to do is attach the auxiliary light to your vehicle, connect it to your battery with the included wiring harness and then run the switch into your cockpit. Some drilling may be required on select vehicles, but nothing that'll faze any do-it-yer-selfer.
OEM replacement lights require fewer steps and no drilling. Just detach the old lights and pop the new ones in their place. It's just that easy.
Fog lights should be mounted low on your bumper because they work best when they are close to the ground. The recommended mounting height is between 10" and 14" off the ground. Most vehicles have openings in the front valance specifically for fog lights.
Driving lights are usually mounted higher so that they can be inline with your headlights. Generally, they should be installed between 14" and 30" off the ground, depending on your vehicle. Driving lights can be mounted almost anywhere on your vehicle. Some of the most common spots are on top of the bumper, on grille guards, on billet grilles, on roof-mounted light bars, on roll cages and even on roof racks. Check with your local laws before you mount them because many states have a height restriction on lights for street use.