From Emacs, you can get help for any key by pressing C-h k and then entering the key combination that you want to know about. Pressing C-h k C-x # returns this:
C-x # runs the command server-edit, which is an interactive compiled
Lisp function in `server.el'.
It is bound to C-x #.
(server-edit &optional ARG)
Switch to next server editing buffer; say "Done" for current buffer.
If a server buffer is current, it is marked "done" and optionally
saved. The buffer is also killed if it did not exist before the
clients asked for it. When all of a client's buffers are marked as
"done", the client is notified.
Temporary files such as MH files are always saved and backed
up, no questions asked. (The variable 'make-backup-files', if nil,
still inhibits a backup; you can set it locally in a particular buffer
to prevent a backup for it.) The variable 'server-temp-file-regexp'
controls which filenames are considered temporary.
If invoked with a prefix argument, or if there is no server process
running, starts server process and that is all. Invoked by C-x #. C-x #
runs the command server-edit, which is an interactive compiled Lisp
function in 'server.el'.
Similarly for C-x C-c
C-x C-c runs the command save-buffers-kill-terminal, which is an
interactive compiled Lisp function in `files.el'.
It is bound to C-x C-c, .
(save-buffers-kill-terminal &optional ARG)
Offer to save each buffer, then kill the current connection. If the
current frame has no client, kill Emacs itself.
With prefix ARG, silently save all file-visiting buffers, then kill.
If emacsclient was started with a list of filenames to edit, then only
these files will be asked to be saved.