Skill-wise this is probably the hardest achievement in the entire game and it is right at the first level. You will only have a pistol for this so make your shots count.
There will be four vents, one in each corner. There will also be Nosalises(monsters) coming from holes out from the ceiling, but you can just ignore these. Your goal is to kill the Nosalises before they bang open the vents. Note that all vents need to stay closed for the achievement to unlock.
Usually you can kill with one shot so keep that in mind. Make sure to keep turning the camera so that you watch all vents. About the same amount of Nosalises will spawn behind each vent(3 to 4).
This video gives a clear view of the situation:
One tip I can give is that you can turn on hit-markers in the options menu. This will make it slightly clearer if you hit your target as it can be hard to spot behind the vent.