How to I export it to make it playable once I download it?

First you need to have the desktop version version of quest downloaded for windows. If you have already been using the desktop editor, then go over to the "play" tab at the top, and under recent it should show your game, and you can play it. If you have been using the online editor, but you have a windows computer, after you download the desktop editor, you need to click on "open an existing game", and it should bring up the files of your computer where you can select your downloaded game. Then you will be able to open it, and play it. If you do not have a windows computer, and you have been using the online editor, I believe your only option is to play the game online. Hope this helps.