Fire Extinguishers: Overview 

In this video, Tim walks us through the fire extinguishers on the different apparatus -- their intended uses and the pros/cons of using each.
Water Can- Only to be used on Class A fires (ordinary combustibles)
Dry Chem- Commonly referred to as an ABC because it is a multi-purpose extinguisher for Class A, B (flammable liquids/gases), and C fires (electrical).
Purple K- Mainly grease fires (restaurants/kitchens).
3% Foam- Good for deep-seated fires (mulch, brush, etc.); the foam helps the water flow deeper into whatever object(s) are on fire.