How do I buy a Shotgun?

I live in upstate new york and im 18. At the end of the semester (january) im moving out of my moms house and into an apartment in schenectady. Anyone from New York knows that schenectady is a shady town, the level of drugs and illegal in the city is pretty high. In fact crime in general is pretty bad in the city. Because of this i want to buy a shotgun for self-defense and was wondering what i have to do to go about getting it done. Do i need a license? Do i have to take cles...