modeling a hand (Blender Masterclass Book)

I am trying to follow the modeling of a hand in the Blender Masterclass Book of Ben Simmonds.

In the picture below I want to get from step 2 to step 3.
The author says: For the middle one I simply selected half of the hand and extruded out.
I succeeded in doing that.

Then the author says: For the outer two gaps, I extruded in the middle 4 faces on the bottom half of the hand on both sides as well as those connecting the two sides along the bottom for a total of 10 faces.

How do I extrude in?



Top row: the middle extruded, and for the bottom faces first extrude, cancel move, then scale along two axes by excluding one with shift+axis
Middle row: alternatively could bevel the middle edge loop with ctrl+B and inset the bottom faces with i
Bottom: or could select and bevel the edges

Whichever way you choose, adjust the face sizes before extruding the fingers out

Thank you very much JA12.
First I extruded the middle (top row example).
Then used inset for the bottom faces (middle row example)
At last I adjusted a few edges to get it exactly as in the book.