1. Go to Halo Waypoint (I assume you already have that downloaded)
2. Click Start
3. Click X, it should bring you to a screen with just large colored circles
4. The circles correspond with your Xbox controller buttons (Green = A, Red = B, Blue =X, Yellow =Y)
There should be around 4-7 circles, click the corresponding buttons on your Xbox controller moving from left to right.
5. If done correctly it should bring you to a screen that has a bunch of symbols, now you must put in the codes found at the end of each terminal.
Lucky for you I took the time to upload the Terminal codes to YouTube so you don't have to look through every fricken terminal and write it down on a notepad.
http://www.youtube.com/watch?v=4ZH7Cc8QOnc
After you enter a code, click the enter option and if you get it right it will flash blue if I'm not mistaken and will give a message saying you got 7,000 credits and blah, blah, blah.
NOTE: after you get the first terminal correct you wont have to do the circle thing again, there should be an option somewhere there that gets you back to the code screen to enter the next code.
Repeat the process and put in all 10 terminal codes and once you get them all in you will unlock the 11th Terminal to view via Halo Waypoint.