How do you make a key open a door?

Ok, thanks!

When adding level triggers to my map's cfg, is it necessary to add the " " marks at the beginning and end? Example: "level_trigger_1" or level_trigger_1 Sometimes I have to keep testing the triggers all day until they finally work. In one of my maps, it worked with the " &qu...

I mean like if you touch thorns, you lose health.

Is it possible to create a health bar that can decrease every time you lose health? If this is possible, how do you make the player respawn if the health bar reaches 0%?

I believe this is possible.

Can you please display the correct cfg for this? I want to use it in my project.

I don't mean like making an object invisible. Suppose a path is blocked by a mapmodel. When you press a button, or activate a trigger, the mapmodel vanishes and you can now go through the path.

How do I make my mapmodels disappear? Not like deleting them in edit mode. Like making them disappear not in edit mode(Like Playing or testing the game).
I think it needs some kind of script.

If the file I downloaded was "Rifleobj.rar. Is the rar significant, or will not apear as a mapmodel?
Am I supposed to convert the file?

What's an mlt file?