The following documentation discusses invoking the debugger, choosing files, choosing modes, stopping the debugger and some essential shell commands.
The essentials are starting gdb and quitting gdb.
Type gdb
to start the debugger in a graphical ineterface mode or use the command,
gdb -nw,
to start the debugger in a non-window interface mode.
Type quit
or use the keystroke sequence, C-d,
to exit.