It looks like the guy kind of shows it in his video, though not too clearly.
There are many different options but the most used is generally a clean plate with a locked off shot for a few seconds, then step in to frame and cut where you want the person in or out.
Green screen provides other options as well as some roto work for the disappear part over the top of the plate.
Here's a tutorial I found on youtube and there are probably hundreds on it but this looks to be detailed.
This should get you going.