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The teacher in the video does go very fast and it's hard to follow all the steps. In the time range you are asking about, he added a chamfer to the top of the hex head of the screw. He did this in 3 steps:
1. he sketched a line defining the position and angle of the chamfer
2. he made a Revolve surface 360 deg, rotating the line sketch about the x-axis
3. he Split the screw head with the surface to remove the chamfer
A better way to chamfer the hex head, is to draw a sketch of the triangular chamfer, and then use a Groove to remove the revolved sweep. (This can all be done with the Part Design workbench, and doesn't require switching to the Generative Shape Design workbench in order to make a surface)