http://www.aa1car.com/library/compression.htm
This pretty much explains it. You'll have to buy one, but tough to diagnose things with out the right tools.
Quote:
To check compression manually with a gauge, all the spark plugs must be removed. The ignition coil must then disabled or the high tension lead grounded. If the engine has a distributorless ignition, the ignition coils must be disabled to prevent them from firing. The throttle must also be held open.
The engine is then cranked for a few seconds using a remote starter switch or a helper while a compression gauge is held in a spark plug hole.
The maximum compression reading is noted, then the process is repeated for each of the remaining cylinders.
The individual cylinder readings are then compared to see if the results are within specifications (always refer to a manual for the exact compression figures for your engine because they do vary from
the ballpark figures quoted earlier).
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Don't really need a helper in the start step, just crank the engine from inside of the cab for a few seconds.. I would check condition of plugs before buying compression tester also, doesn't hurt to check spark plug wire resistence either.