In order to unlock two of the achievements of Halo 4 , Contact the command and Terminus, you must find all the terminals in the game campaign.
Below you will find a video that will show you step by step how to retrieve all seven necessary terminals.
Towards the end of the mission, after defeating two Hunters (the armoured enemies), you will be able to access the tower. At the end of a long corridor you will see a large semi-transparent ramp. Under this ramp you will find the first terminal.
Immediately after defeating a group of Prometheans (a few minutes from the start of the mission, depending on the difficulty), you will notice a large structure with rock walls on both sides leading to the entrance. As soon as the Master Chief asks Cortana, "What is the distortion?" as far as his HUD is concerned, you'll find yourself in front of the terminal, located on the ground.
Immediately after the scene where you meet a group of friends, just look around.
Exit the room where you ask Cortana to find an elevator directly in front of you. Instead of going up immediately, look down the corridor to the right to find a terminal.
After Cortana has reached the waypoint, instead of turning right to reach it, continue further to the large structure at the end of the room. Just in front of it you will find another terminal.
After the film where the Master Chief meets Dr. Tillson, you will see the Atrium in front of you. Move your gaze over the building to the right and you will find the terminal among the jagged rocks.
Once you are on 'earth' you will proceed through a series of rooms. In the third room, behind the central pillar, there is a terminal.