It's a quick editing trick that will elevate the quality of your video to a professional level that we're used to watching in commercials, music videos, television, and movies.
Click "Music" and select a background music track from the library or upload your own.
Click "Beats" to reveal music notes above the timeline; the orange notes signify the first beat of each cycle and the gray notes signify other beats in the cycle.
Using the handles on either side of each asset, click and drag to the preferred music note for the change between assets to sync to the musical beat.