123td1234: What editing software do you use? If you’re using Adobe Premiere Pro, press Command + I (or Control + I if you’re on Windows) to open the option to import a file and then the file browser will open. Just locate your music file and double click it to add it to your project. Then in your main project view where all your other video files are located, click and drag that audio file on to your timeline. It should be the same or at least similar for other editing software like iMovie and Final Cut Pro, although I’m not exactly sure since it’s been a while since I’ve used iMovie and I’ve never used FCP.
What would also be useful would be to look up some YouTube videos on how to edit. I am on mobile so it’s gonna be difficult to link them but once I get on my computer I will edit this further