Okay, i'll give you a described example of how to use switches.
1- In any map, let's use a house, create a new event, i'll refer to this one as E1 from now on, and set it to Auto-Start.
2- Now create a new event for where we want our NPC to spawn, just place in front of a door or steps, don't set an image for it.
3- In E1, create a "Move Event" command, change the image of NPC to make him visible, and then create some movement commands to make him go to you.
4- Make him say something, and again set some movement commands to get him out of sight.
5- In E1, create a new switch and turn it on, also, call the switch "CONVO1" or something, anything that you'd like, it doesn't matter.
6- Now, in E1 again, create a new page, and on the left hand side, in the "Preconditions" menu, check one of the Switch boxes, and select "CONVO1" or whatever you called it. Make sure the image is blank and now make him "Below Hero" in the Event Layer, so you don't get stopped by his invisible sprite.
There, a basic guideline on what you need to do with Auto-Start events. So when you test play, walk into the house, and this short scene will automatically happen, and will end without any eternal loops.