You want to make things move, interact, explode, break, kill NPC's and many more things just by looking at them? Here's the tutorial you want.
For A Door
Make a small room (for example purposes) and add a info_player_start entity on one end of the room. In the middle of the room, make a wall and cut out a piece for a door. Put your door inside the hole and name it lets say door1. *This is not a tutorial to make a door, if you don't know how to make a door, find a different tutorial and then refer back to this one.*
Now make a box with the trigger texture on it that covers all up and down the room and from the door to almost you. Leave some space between you and the trigger so you will have to walk into the trigger to make the door open. Press the toEntity button or double-click the box and in the Class: field type in trigger_look and press apply.
Next, go to the Outputs tab and in the My output named scroll down to OnTrigger ans click it.
On Targets entities named, scroll down to door1 - or the name of your door - and click it.
On Via this input, scroll down to Open and click it.
Leave After delay in seconds of alone. Do NOT click the Fire once only button. Press apply and go back to the Class Info tab.
Make sure Start Disabled is on No. On Look Target put the name of your door in my case door1. On Look Time put in how ever many seconds you want for it to take to look at until it reacts. That is all for the door. When you run your map it should open when you look at it.
Use this technique for any other object you want to react but make sure that you use the right action in the input on the outputs tab.
Making the enemies die when you look at them is somewhat complicating, but so worth it considering they fly in the air and die. It's fun to play with. Here is how you do it.
Make a small room (for example purposes) and add a info_player_start entity about 1/4 the way from the wall. Now place how ever many NPC's you'd like in front of your player.
*Note: I got the enemy kill from an awesome game called Mistake of Pythagoras and don't actually know how he made the phys_ragdollmagnet like it is in the game, so I copied the items and pasted them in my game, so if you want to kill enemies by looking at them, then go to my example map at Moddb.com and download the file. Zip it and go into the folder and find the .vmf file and open it in hammer editor. Copy the enemy and the green target behind it and the trigger box in front of the enemies(don't copy the Ai's) and put it in your room. I'd suggest you just keep the name and everything inside it the same because one false move could mess it up.*
Once the enemy and the green target and trigger are in your map run it and it should be good to go. The example map also contains the doors that open when you look at them. Make sure you get the right trigger there are a lot of them. The right one is the one that is kinda showing through the doors. I'm sorry I can't tell you how to do this yourself, but taking it from my map is still easy and makes it all fun. You can change the NPC type too it is not limited.
Have Fun. Thank You for checking out my tutorial. Hope this helps.