Open iMovie from your dock or search for it in your Launchpad or Spotlight
Select Create New and choose Movie.
Click on the down arrow to import music files, photos, and other videos (or drag files directly into your timeline)
Select FaceTime HD Camera in order to record yourself
Drag everything into your timeline
Start editing: add titles and transitions, etc.
Click on the picture above to export your iMovie projects in order to upload them to YouTube or Canvas.
Resources from Apple on how to use GarageBand to create audio recordings, which can then be imported into iMovie.
Click on the image to access Adobe's Premiere Rush User Guide for making videos.