The central beam weapon of an Ori warship was an extremely powerful weapon that discharged fiery blasts from a central dish located at the front of the vessel. The beam fired by this weapon was capable of destroying a Ha'tak with a single strike, piercing its shield and ripping through the vessel while still retaining some power. The Ha'taks were completely useless against Ori warships; fleets of them could barely even slow down a single Ori Ship. The Asgard shields on Daedalus-class vessels were far more resistant to the weapon's blasts (due to their far superior technology), but multiple strikes would deplete the shield and eventually destroy the vessel (the Tau'ri were later gifted with even more powerful shields of Asgard design but they were shown to be drained rapidly by the beam as well). The beam weapon usually took a few seconds between firings to recharge.
During the Ori crusade, this beam weapon was arguably the most powerful ship-mounted energy weapon ever encountered until the development of the Asgard plasma beam weapon, which proved to be equal to the Ori beam weapon in effectiveness. 
The only known downside of the Ori beam weapon was that it caused the shields of an Ori warship to fluctuate whenever it was fired, allowing external Transportation rings to connect to the Transportation rings aboard an Ori warship and vice versa. 
Like the power crystal from an Ori staff weapon, the beam can be used to power other technology. However, for this to work, it must strike the ship with the technology on it, destroying the ship but channeling the energy through the ship's power conduits to the technology. This was used to power a reverse time field with the time dilation device in the Asgard computer core to reverse the 50 or so years SG-1 and Major General Henry Landry were trapped on the Odyssey. 
The central beam weapon was controlled by a Prior, who does not have to be seated in the control chair to operate the weapon. As a result, it is believed that the beam weapon is controlled via the Prior's staff.