These apps can help you edit the photos and videos you take on your phone into something more shareable.
Google Photos - I highly recommend backing up all of your photos and videos to this free app. It can also help you create movies from your media. Just select a few items, then click the "plus" sign in the upper right-hand corner of your screen and select "Movie."
Adobe Premiere Clip - This is a like a tiny version of the program the pros use to edit TV shows and movies. Just select a few clips and you can let the app do all of the work or you can get super specific with your own edits. This app can give you the most professional looking results.
Magisto - A fast and easy way to make stylized movie creations. Select a few clips, plus a theme and music and you're on your way to a sharable clip. Magisto does most of the work in the cloud so it might take a little longer to process and produce your final creation. Start here for the easiest way to create fun little movies to share with family and friends.