The other Pencil-Hand ... what will happen?

This morning I wanted to find out what would happen when I click on the pencil-hand in the block top bar, which I was too timid to try last night.  Here is where I started:

Here is the pencil-hand I clicked this morning:

... and KA-BOOM!  Near-instant and radical change to the screen display, now showing what is below:

I will go to Moodle Docs to figure out all the things I can do from here.  What a difference a click makes!