How do I Send Expiring vs. Non Expiring media?

To send media tap the plus sign in the bottom left hand corner of your chat.

Now you can send photos, videos, YouTube videos and photos from your camera roll.

To send an expiring photo, select the number of seconds you want it to show up by tapping the clock in the upper right hand corner. If you don't want your photo to expire then tap the infinity symbol. 

For videos Select either "non-expiring" or "expiring" by tapping the right hand corner