Information gathered from TF wiki
Vehicle mode: Pyro is split into 2 half, red cab (front) and yellow cabin (back)
Pyro's gun which looks more like the fire engine's deluge gun can be mounted onto the front cab. The 6 turret missile launcher would be activated during battle. Back of the cabin opens up to transport injured Autobot to safety.
Base mode: Back cabin can be transform into a battle station having the same concept as Optimus Prime. It consist of a 5 turrent missile launcher and a control station.
Lets look at how Pyro transforms from a airport crash truck to the defensor of earth....