CheckEngine light on Explorer 96 XLT

Check Engine Code P0420

I need help to fully understand this code. I took my 96 explorer XLT to Autozone for a "checkengine" light. The code was P0420, and this is info on the paper:

The PCM has determined that the catalyst system efficiency for bank 1 is below threshold for the current engine operating conditions. (Bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank)

Definition: Catalyst efficiency low-bank 1

Explanation: the oxygen sensors monitor the catalytic converters ability to store oxygen.

Posible Causes:
1.Catalytic converter defective (Failure posibility due to #2, 3 or 4)
2.Engine misfire or running condition
3.Large vacuum leak
4.Engine oil leakage into exhaust-valve guide seals, piston rings.

I was told this truck has 4 catalytic converters. Is it true? I was told by somebody else these are expensive.

Does anyone have a diagram or picture of these converters? I would like to know which one is the bad one, and also learn & try to fix the possible cause of this. How can I know if I have a vacuum leak? Engine oil leak? I normally do not use this truck, so I can not really tell.

Also, how can I reset the check engine light?

I am kind of broke right now, so if anyone could share a service manual, I would be more than happy