There is often a terminal just inside the main gate (opposite where your taxi/iown ship lands), just off to one side. Go to that or any other terminal you can find outside. Choose the section showing the different buildings and look for the Habitat. There will sometimes be two, but often one is just contains a cabin. If you know what part of the HAB you need (corridor, dorm etc), choose that in the next column. When selected you will then see the contents of each room and somewhere will be an object showing the blue mission symbol. Click on that and a pin will appear on it. Leave the terminal and check your top HUD, turn until you see a blue/orange marker with distance, and head towards it. The object itself will also have a round marker on it at the height it is above ground, so if the round marker appears high up, you know it is upstairs. Once you are at the position indicated by the HUD marker you will usually see the round marker nearby, either at the same level or slightly above, indicating the upper floor. When you arrive at the settlement, a message will appear in the top right corner reminding you of the mission and giving the code number. Interact with the padlock and enter the number in the display using arrow keys to move around the keypad, then press the enter key in the bottom right and the box/locker will open. Interact with the required object inside and you will pick it up. If you are feeling brave, you can check open boxes and lockers for other objects and take (steal) those too for some extra credits - but don't get scanned if you do!
PS - keep a close eye on that text in the top right - that is where you will see when a guard is targeting you for a scan and STOP until you get a scan clear message (if you have nothing to hide of course - otherwise.... well good luck LOL)
