You build up experience to the point that you get to a new level, and get rifle training. You probably need to go up 3 levels - each level requires 25 more XP than the previous one. So, go deer hunting in the surrounds of York, or attack your fellow citizenry (although that leaves you with the rep of being a PKer and you'd probably not be welcome in the tavern or elsewhere in York).
Bear in mind that when you kill a player or animal, you not only get the XP for the attack, but extra bonus XP upon their death. Successfully attacking gets easier the higher you go by level.
