I think what they mean is that the PCM will "learn." The PCM monitors every aspect of your truck, including your driving style (i.e. short trips vs. long trips, speed, distance, etc.) and analyzes the stored data. It then makes adjustments (such as air flow/fuel flow) to get the most ideal performance from your truck's engine and components for what the PCM has determined to be your "driving style." Keep in mind that the PCM will "learn" this information and adjust your engine components whether it is correct or not. For instance, if you had an aftermarket air intake, your PCM should have calibrated your truck to run at optimum performance with the intake; removal of the intake may cause your truck to run erratically if your PCM does not re-adjust for the change in air flow.
I hope this makes sense, I sometimes ramble when I try to explain things.
