understanding the 'extrude'?

[Misty Wisty]

i'm not actually making anything at this point, just trying to understand what the commands do exactly. save on frustrations later on

i used hole so i could see better what the extrude was doing. by extruding all the faces but the one, i was making a new enclosed mesh.

hmm, alternatively, i could extrude all faces but the one and then loop cut out the one face. testing ...