This video shows what a Faucet Cartridge looks like, and how it works. I show how to replace a Cartridge on a Price Pfister bathroom faucet from the Pasadena collection. Some other brands use cartridges, and replacement is similar. The cartridge is free via Pfisters lifetime warranty. Pfister has a lifetime warranty, and replaced my handle and cartridge free of charge when it started to malfunction.
If you need a cartridge sooner, Amazon carries it:
Cold water cartridge: http://amzn.to/2jTyOmJ
Hot water cartridge: http://amzn.to/2jVvzLd
Brass retainer nut: http://amzn.to/2AW1e9S
How to replace a stuck or hard to turn faucet handle: https://youtu.be/nFQfxb1PbJc
Music: http://www.purple-planet.com