In the viewfinder, tap the video thumbnail at the bottom of the screen.
The last video you recorded appears on the screen.
You can also scroll and select other videos to watch. Your Gallery videos (and photos) are displayed in film-like images at the bottom of the screen for you to select.
Tap the Play icon in the middle of the still image of the video to play it automatically.
Open the Gallery application, then tap the album you want.
Tap the video you want to watch to play it automatically.