This specialized training device primarily raises Strength, Speed, and Offense. Secondarily it will give BP and Energy. All you have to do is face the proper direction and attack it.
The gains of peebags are more then the gains of Meditate Level 2 as well as that of the Train Verb. If your stats are capped it is good to use a Peebag while flying although it'll drain your energy faster, it will also still increase your gains.