This isn't really intro, but I love the combination of interesting terrain, map with GPS, and an amazing orienteer (Tove, in Spain) actually orienteering.
I also use this one, for the first couple of minutes. Clear explanation, and cute. My middle school kids appreciate that it was made by an 11 year old. I appreciate that it covers the basics clearly.
And if you want to show the international level, I like the intro from :40 to 2:20 of this:
It's a straightforward explanation, with WOC clips, and a few map clips. And it shows the competitive aspect of the sport. I'm going to show all 3 today, as there is snow on the ground (again).