When you log on you will see trending GIFs as well as categories above to search. If you would like to see one, simply select it and then you will see it play and you can hear the music by selecting the audio icon. You can share it by selecting the share icon in the bottom right. You can also save this as afavorite (upper right heart) as long as you are logged in with an account (you can use Facebook).
If you would like to make your own just select the photo/meme/GIF you would like to use and then search for the music that you would like to accompany it.
Embedded below is a 1 minute and second YouTube tutorial.