It's the yellow icon with a white ghost. Videos can last up to 10 seconds. If you haven't turned on filters, tap Enable Filters to access the special effects. The snail plays your video in slow motion, while the rabbit speeds it up. The three backwards arrows plays your video in reverse. Some filters change the color or brightness of the screen. Other filters add effects such as your current speed, location, or time. Some filters, such as the snail and rabbit, cannot be combined. It's the white right-pointing arrow at the bottom right of the screen.

Summary:
Open Snapchat. Tap and hold the large circle icon to take a video. Release your finger when your video is complete. Swipe right or left to add special effects. Hold one finger down and swipe another to combine filters. Tap the "Send" icon. Tap on a recipient. Tap the "Send" icon again.