You unlock doors by finding keys for them, or by finding levers to pull, or, less frequently, taking some other necessary action such as talking to someone who can open the door.
You left out one critical piece of information - which level are you where you are getting killed?
My guess is you are right near the beginning, and have just unlocked a door using the 2431 combination of levers as you were told to do. The note telling you this refers to something else you should do - and you might note that there is a 5th lever.
These aren't the last traps you will find although there are no more for a while - it may help to get find traps skill for 2 points so you can see them. (2 points suffices for act 1)
