why are there many terminals and what is the point of those specially gnome terminal and virtual terminal
gnome-terminal are simply two different kinds of "terminal emulators", i.e. they make it look like you are on a real terminal (=text mode linux), but are designed to work in a GUI environment. xterm is the classical X11 terminal, while gnome-terminal is Gnome's default terminal.
The difference, apart from visual appeal, is that gnome-terminal has many more features than xterm but also requires you to be running Gnome. There are many more terminals of this kind available: xfce4-terminal, lxde-terminal, etc., with different looks, different feature sets, different dependencies and different "weights" (i.e. how much RAM they consume).
The "virtual terminals" (Ctrl+Alt+F1 to F6) are "real" terminals, not terminal emulators. If your regular desktop (Gnome) is ever in trouble, or you are having problems booting, you can try switching to another virtual terminal so that you can log in and try to fix the problem (in text mode).
This is a real terminal, as larsmans pointed out: