Hey man how do I open a quest file?
Viewing post in The Lab: Mutations jam comments
You need to install the Quest software to be able to run it, there is a link in the install instructions, then you just double click on it and it should open! :)
Alternatively you could try to play it online (link also in the install instructions) but be warned the website hosting it can be laggy at times
If you need anymore help feel free to ask!