What does an air filter do? Why purchase one?
An air filter protects against debris from getting into your engine. The factory air filter on your car is very restrictive, and buying an performance filter will generally help improve throttle response and add a pleasing induction sound to the engine under acceleration. An air filter can also significantly clean up the under-hood appearance of your car and make it easier to see and access components of your engine bay.

How do you install an air filter?
It depends on what type of car you have and what type of air filter you get. A drop-in air filter is installed by opening up your stock air box, pulling out your factory paper filter and replacing it with the new high flow unit. If you opt for the open-element air filter, then your whole air box should be removed and replaced with the new filter. If the filter is universal (not vehicle-specific), slight modifications using reducers and couplers may be needed depending on the size of the filter and intake hosing.