Let's assume I want an actor of the High Elf race to have a special idle animation (I think there are several unique ones already present in the game, right?)

Where can I find these animations and how do I apply them to my NPC?

Look under gameplay->animations and then expand character for a list of all the vanilla idles.

To get one of them to play use actor.playidle(idle_property)

There can be issues with some of them, if the proper conditions are not met, or if they're busy doing something else.

If you want to add new idles, that's a whole 'nother discussion

Okay thanks!!

About the "actor.playidle(idle_property)"-part, should that be located in a script? If so, where should that script be attached and how should it be written? I'm a complete newbie at scripting ^^

That pretty much depends on where you want to trigger the animation.

If you want someone to start doing when FooQuest reaches stage 10, you could add it as a fragment for stage 10 in the stages tab or the quests window.

Although better practice is to create a script for the quest, and give it a function to start the animation. Then you can set kmyquest in the fragment box and call the function from there.

If you want it to trigger from an activation box, or a dialogue info, same basic procedure.

(That's kind of a high level overview - ask if you have more questions )