If you want to login to a remove computer, you can do that just as you would expect, using whatever commands you would normally use.
(This is worth emphasizing, because earlier versions of shell
mode would not work properly if you tried to log in to some other
computer, because of the way echoing was handled. That is why
there was a separate telnet mode to partially compensate for
these problems. The telnet mode is no longer needed, and
is basically obsolete.)
A program that asks you for a password will normally suppress echoing of the password, so the password will not show up in the buffer. This will happen just as if you were using a real terminal, if the buffer is in char mode. If it is in line mode, the password will be temporarily visible, but will be erased when you hit return. (This happens automatically; there is no special password processing.)
When you log in to a different machine, you need to specify the
type of terminal your using. If you are talking to a Bourne-compatible
shell, and your system understands the TERMCAP variable,
you can use the command M-x shell-send-termcap, which
sends a string specifying the terminal type and size.
(This command is also useful after the window has changed size.)
If you need to specify the terminal type manually, you can try the terminal types "ansi" or "vt100".
You can of course run gdb on that remote computer. One useful
trick: If you invoke gdb with the --fullname option,
it will send special commands to Emacs that will cause Emacs to
pop up the source files you’re debugging. This will work
whether or not gdb is running on a different computer than Emacs,
assuming can access the source files specified by gdb.