How to add music to a video

Hi @Shahjon

and welcome to this Apple (user-to-user) Community!

Re: "iMovie: how to add music to my video"

Apple support's online article (link below) explains how to:

"Add songs from your music library"

or

(scroll down) "Add other audio files

You can add audio files like M4A, MP4, MP3, WAV, and AIFF files stored on your device, in iCloud Drive, or in another location".

See: Add songs and other audio files to your iMovie project