How do I know if I have a short circuit
I would highly recommend using a digital multimeter in this case. They are not too expensive and a must for electrical projects. Most have functions such as checking for shorts. In addition, you can check to see if the pin in question changes voltage when activated. The thing to remember is that heat kills electrical components, and high current causes heat (high power, really, but watch your current and you will be fine) get familiar with the formula v=I/R and don't put too much current through your buzzer or LED. LEDs have very little resistance.