Glossary
B-roll
Supporting footage laid over speech: you still hear the person, but you see what they are talking about.
B-roll is cutaway footage: hands kneading dough, a software screen, an empty gym in the morning. The sound of the main take carries on underneath; only the picture changes.
In a short video it does two jobs: it hides a cut that would otherwise make the image jump, and it shows what is being said instead of just saying it. A lone face, for too long, gets tiring fast.
Good habit: on every shoot, film about ten silent seconds of each gesture and each place. That stock will serve you for weeks.
A baker explains her sourdough; while she talks, you see the dough rising and the crust cracking.