My goal is:

Make an NPC talk to an other when the player goes in to the trigger (the blue box), but just when a specific stage of my quest is donne

This is what i've done at the moment:

- Created a quest

- Created a scene

- Created a trigger with the following script

Scriptname SCVtriggerscript extends ObjectReference  Int Property SCVTriggered  Auto  Quest Property Myquest  Auto  Scene Property MyScene  Auto  Event OnTriggerEnter(ObjectReference akActionRef)   if akActionRef == Game.GetPlayer()      if SCVTriggered == 0        if Myquest.GetStageDone(25)            SCVTriggered = 1             MyScene.Start()         endIf      endIf   endIfendEvent

SCVTriggered doesn't need to be a property. You can just make it a local variable (change it to Int SCVTriggered). It's explained in my tutorial http://skyrimmw.weebly.com/skyrim-modding/creating-a-do-once-script-skyrim-modding-tutorial.

Oh! didn't know about that web! Thanks a lot. By the way, my script is not working, do u know why?

You'll have to be more specific than that. What about it isn't working? If the scene isn't starting, make sure you've filled all your properties (via the Properties box and then selecting scene/quest from dropdown after highlighting the property). If it still doesn't work add a debug.notification somewhere in your script to check which part isn't working:

Scriptname SCVtriggerscript extends ObjectReference  Int SCVTriggeredQuest Property Myquest  Auto  Scene Property MyScene  Auto  Event OnTriggerEnter(ObjectReference akActionRef)   if akActionRef == Game.GetPlayer()      if SCVTriggered == 0        if Myquest.GetStageDone(25)             SCVTriggered = 1             Debug.Notification("Got to the scene part. Scene not started yet.")             MyScene.Start()         endIf      endIf   endIfendEvent