showing 2 buffers m then x

[Baloff]

Hello

reading GNU Emacs by O'Reilly, in the buffer list, m to mark 2 of the
buffers I would like to show, then x which suppose to execute the
selection, but according to my C-h m while in the buffer list shows
that x -- delete or save marked buffers.
I am working with 21.4a-1, 21.3.5 is what the book covers, so I am
guessing that the x key in 21.41.1 differ. is that correct and if so,
what is the execute command once you mark your buffers?

thanks