Record your instruction for many purposes
You may have heard of Flipping the Classroom but there are other reasons to record a lesson for your student's to watch. You might have a concept you need to teach but you're going to be in a meeting that day. Perhaps you know your students are struggling with a concept and you want them to be able to access your lesson any time. Or, you might make a lesson to help review for a test or for students who are absent.
Record what's going on on your computer while you also record your voice - and even a little video of your head in the bottom corner.
Record yourself teaching the lesson capturing the whiteboard and yourself.
"Smartboards" can record your marker strokes - I'm not sure if records sound.
There are many apps that let you - or your students share what they know.