How Do I Connect 2 Screens Namely a VGA and HDMI?

I have 2 screens namely a Samsung VGA connection as well as a Dell HDMI that is connected to a thunderbolt (Unitek) with DVI, HDMI, Audio and VGA ports, once I connect the screens and i go to settings and then display I only see 2 screens, namely my MacBook Air as well as another screen and the tow monitors have the same information on it, how do I go about it to get it fixed that I see 3 screens?
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Nic