When you first stumble upon GTFO, it can seem daunting - a vast underground sprawl filled with mysteries and monsters. Fortunately, there are The Terminals dotted around the level to help you out. The terminals will appear as a red kiosk with a screen, and you can interact with them by holding the "E" key. When you log into the terminal, you will see the root, and from there you can use various commands to find useful items in the level.
LIST
The list will cause the terminal to display a list of useful items found throughout the level. These include The keys you will need to open the doors, The ammo packs, The medipacks and anything else you might find useful.
QUESTION
Using the item code that you found with the List command, you can then type Query, followed by the item code, to find the exact location of the item. For example, if you need a specific key to open a door with the code KEY_GREY_473, you can type QUERY_KEY_GREY_473 and the terminal will tell you the exact location of the key.
This allows you to search for the location on your map and head straight for the area, rather than blindly searching through the level, which could potentially threaten you.
If you arrive in the area where the item is located, you can also use the Ping terminal command, followed by the item's code, to ping its location, which makes it easier to find.
You will still have to explore the map to find the right area, the terminal won't do all the work for you. Just make sure you move slowly and carefully around the areas, and try not to trigger any alarms.