The Portal computer terminal was a display system created by the Lantean's.
These were large flat computer screens the size of a table which contained information on their surface and were connected to Atlantis through the Lantean observation satellite. Through it, the inhabitants of a planet were capable of being provided instructions from scientific fields to militaristic data allowing for the Human civilization to be slowly developed. This made the human inhabitants believe the portals to be holy relics with instructions being provided by the Oracles themselves.
It was possible to tap into the portal system and feed them false information.
During the time the Ancient's inhabited the Pegasus galaxy, they placed portal computer terminals on numerous worlds with Human life in order to guide their development. The computers deactivated after the Lantean-Wraith war as the Lanteans left for Earth resulting in the portals being silent on worlds such as M4D-058.
When the Atlantis expedition arrived in Atlantis, they discovered the Society research lab which they believed was a game room and not real civilizations. Through the room, Lt. Colonel John Sheppard and Dr. Rodney McKay gave their two societal inhabitants of M4D-058 orders on how to develop their civilization in competition with one another. However, the two became antagnostic to one another leading to increasing hostilities.
After discovering what the "game room" was, the Atlantis Expedition helped prevent the destruction waged by the two human races by hacking into their portal computer terminals making them believe that they had mutually destroyed one another in order to show them what were the possible outcomes if they continued their conflict. (SGA: "The Game")