http://codinghorror.typepad.com/.a/6a0120a85dcdae970b0120a86d9495970b-piAn image to explain what FOV is and how it's used.
TIPS:
1. The smaller the FOV, the more your view will be ZOOMED in, which means that objects will appear much-much closed than they really are.
2. Human eye has a 120 degree FOV but it's not right to put that into effect.
3. FPS games usually go from 70 to 100 degrees, while Flight sims go from 45 to 70. Strategy games may go to 110.