This button usually allows you to send pictures from your gallery in the Snapchat messenger. When this gallery button turns blue that means that you and the person you are messaging are both on the same screen. When this happens you can hold down the blue button which will start the facetime feature. When you press and hold the button you it will first display a circle containing the view of your front facing camera. As soon as you hold down the blue button the view from your camera will replace the messages on the other users screen. There will be no audio until the other member presses and holds the blue button. Once the other user presses and holds the blue button on their screen. The messages on your screen will be replaced by the view from their front facing camera. The facetime will end when either one of the participants leaves the message page, or both participants remove their finger.
Congratulations, you are now Snapchat facetiming. There are a few little tricks you can do once you have initiated the facetime with your friend. The first one I am going to mention is flipping the camera. To switch between your front facing camera and your regular camera, you have just have to slide your finger to the top half of the screen this will flip the camera from front facing, to normal. To switch it back, you just slide your finger back to the bottom half of the screen. It can be kind of tricky at first, but once you get the hang of it, it will be intuitive. The second little tip I’m going to give you is how to lock the facetime so that you do not have to hold your finger down the whole time you are facetiming. To lock the facetime just slide your finger to either the very top of your screen, or the very bottom of your screen, your circle with the view of your camera will follow your finger to either the top or the bottom. Then just hold your finger, with the circle following it, at the top or bottom of the screen. When you do this a transparent lock symbol will appear. When it does slide your circle to the symbol; this will lock it in place so that you don’t have to hold it there the whole time. This helps greatly if you are sharing live video for an extended period of time.