Motorcycle Repair: Reserve fuel capacity/1995 Sportster, reserve fuel, filling station

Question
Hello Mike!
I am a new (female) rider and had something happen that I need to clarify ASAP because my significant other apparently thinks I am a complete idiot! I have a 1995 1200 Sportster...I tried to start it and found I was out of gas...I switched "petcock?" (WHICH I NEVER TOUCH ANY OTHER TIME!) to reserve and it started right away no problem...got on and rode LESS than 5 miles and ran out of gas!  My question...why did this happen? Can you explain in simple terms how the fuel tank/reserve situation actually works? I realize Sportster capacity is small...but really, 5 MILES?! What good is reserve if I were in the middle of no where?
Please help me with this little dilemma.  Thanks so much!  Sheryl  
P.S. Yes, I know I need to learn to how to judge gas level better!

Answer
Your petcock has two tubes at different levels. One is on and one is reserve. the reserve is lower than the on position. When you run out of gas in the on position and switch to reserve the tube in the petcock is lower giving you some more gas. the problem is with sportsters is that reserve doesnt go very far.Even on the big bikes you cant go very far on reserve. What you need to do is set your odomemter to how far you can go on a tank and before running out start looking for a filling station.
Good luck and happy riding
Mike