How do I do it? I remember in Fallout 3 there was a list of npcs where you could select them and edit their attributes, but I don't know where to find it in the skyrim creation kit...

Second check box to the left.

Could you stop trolling and give me a real answer?

I don't troll on these forums, or anywhere. I gave you a real answer. That's the only way to set them essential, besides through a script. You can't even do it on the reference in the render window.

Sorry, I believed you were talking about a way to make the npc list appear! Because my main problem is that, when I open the kit, nothing is inside it, and I don't know how to make the various lists appear!

Assuming you haven't done this, you need to load Skyrim.esm and Update.esm.

After that is done, you wanna navigate to the Actors tab. Collapse it, and then collapse Actor.

Big huge list of ALL NPCs in the game. But you can't set their flags in bulk. Gotta be done individually.

As for my first post, I was under the assumption that you already knew how to edit actors but just didn't see the check box(even I miss things so obvious sometimes).

Should I load both skyrim and update?

Update.esm is necessary for official fixes and additions, but not necessary to load up all the references in the game.

Thank you!