Adding a Video to Favorites
When viewing a video, click on the heart icon at the bottom of the screen.
Viewing your Favorites
From there, if you wish to view your favorited videos, minimize current video and/or go back to your main screen:
Tap the user icon at the bottom of the screen:
Tap on "Favorites"
To Remove a Video From 'Favorites'
Option 1. Swipe left on video you'd like to remove:
Option 2. Tap on the video and tap the heart icon again to remove from favorites: