First, you'll need to export your video. After you've done that, you can follow these instructions to download it to your computer or phone:

If you're on a desktop computer, click the 'Download [Size]' to begin a download to your computer's file system:

Note that if you have slow internet, the download might take a few minutes. Once the download is complete, you should see the video in your computer's file system, wherever your downloads are stored.

If you're on a mobile phone, you'll see two buttons: 'Open [Size]' and a 'Share' (a square with an arrow pointing up from the middle):

On iPhones, pressing the Share button will give you the option to share your video to a text thread or app, or to download the video to your photo reel. To download the video to your photo reel, click 'Save video':

If you open up your camera roll, you should now be able to see the video.