Open up your gallery and select which photo you'd like to attach your video to. In the top right corner of the photo, select Embed Video. Paste the URL of the video and you're all set! The video will be displayed on the gallery page of your website.
If you don't have an image uploaded to attach your video to, I'd suggest taking a screenshot from your video, uploading that image, and then attaching the video to the image.
Keep in mind, Bloom supports videos hosted by Vimeo and Youtube. So make sure that the URL to your videos is coming from either one of those websites.