A trainer is a type of cheat.
Trainers are used when a game's "action" is too hard.
For example, I've used a trainer for a different game (not SOMA) and that trainer prevented my character from being hurt. The enemies could whack away (or bite away) all they liked, but they couldn't hurt my character.
The trainer has to be running at the same time as the game, and you use hotkeys to activate the cheat you want for the trainer.
I have not used the trainer for SOMA and don't know how well it works.
The trainer that's available at cheathappens has a readme with instructions
http://www.cheathappens.com/21447-PC-SOMA_cheatshttp://www.cheathappens.com/nfo/soma-readme.txt
Using this Trainer
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Launch the trainer first, then launch the Game and then Press F1 at the Main Menu.
Listen for "Activated".
Press desired option key
Options
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Numpad 1: Invisible
Numpad 2: God Mode
Numpad 3: AI Cannot Attack
Notes
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Numpad 1: Invisible - toggle on and most AI cannot see you.
Numpad 2: God Mode - toggle on and most things that harm you
cannot harm you. Some creatures may also avoid you.
Numpad 3: AI Cannot Attack - toggle on and even if you are
seen, the AI will not be able to attack you in most
cases.
I don't know if you need the "NumLock" on your keyboard to be activated (or not) for the Numpad commands to work.