[Q] In emacs, how to copy a region of the buffer to a string to process ? Urgent

[Fren Zeee <frenzeee@gmail.com>]

This is a newbie question for which I need quick help.

[Q] In emacs, how to copy a region of the buffer to a string to process ?

What are the various available functions and which is the lowest of these ?

copy-region-as-kill
  Command: Save the region as if killed, but don't kill it.
buffer-name
  Function: Return the name of BUFFER, as a string.
copy-to-buffer
  Command: Copy to specified buffer the text of the region.
current-buffer
  Function: Return the current buffer as a Lisp object.
get-buffer
  Function: Return the buffer named NAME (a string).

Thanks
Franz Xe