When you tap on the video in the Gallery, then tap the pen icon to edit, you will see a speaker icon to the bottom left, tap that and besides adjusting video volume, you can also add background music. 
You have another option, and that is again to open a video and tap the pen icon to edit.
Then tap the 3 dots on the bottom right and select Create Movie.
This will then open a new screen and ask you to select the video you wish to work with. Select the video, then you can choose background music, change the aspect ratio and add text.
Then tap the 3 dots on the bottom right and select Create Movie.
This will then open a new screen and ask you to select the video you wish to work with. Select the video, then you can choose background music, change the aspect ratio and add text.
Another option to edit videos etc, is open the Gallery App, select Albums, then in the bottom right tap Videos.
This will then show all videos in the Gallery. Then tap the 3 dots in the top right and select Create, you will now have a menu pop up giving you 3 choices and you can choose to create a movie.
It's much the same thing as above, just another way to get there.
This will then show all videos in the Gallery. Then tap the 3 dots in the top right and select Create, you will now have a menu pop up giving you 3 choices and you can choose to create a movie.
It's much the same thing as above, just another way to get there.
