Pull all the spark plugs out.Screw the guage into one of the holes. Turn over the engine, either by the pull rope or the electric start, 4-5 pulls with the cord- 4-5 seconds on the starter. Repeat for the other holes. Make sure you bleed off the air out of the guage each time. (there's a little valve up by the guage) Compression for an XLT should be around 115-125 PSI, but most importantly they should be even across all the cylinders.
Make sure you hold throttle wfo for accurate compression test. This is reccomended by psi, slp,crank shop and most other high performance shops to get a better idea of engine condition using dynamic compression also.