It's like this:

<Station name="Left Wing Outer" params="-4.0(x),0(y),-0.5(z),0(p),-0.017(h),0(b),200(qty)"/>

X = Left or Right of the Centre of Gravity (CG) of the aircraft (distance in metres)
Y = Up or Down of the Centre of Gravity (CG) of the aircraft (distance in metres)
Z = Forward or Backward of the Centre of Gravity (CG) of the aircraft (distance in metres)
P = Pitch (tilt Up or Down)
H = Heading (yaw Left or Right)
B = Bank (tilt Left or Right)
QTY = Amount/number (Quantity) of ammo/missiles

So that the setting above is:

X = 4 metres to the Left
Y = 0 metres Up/Down
Z = 0.5 metres Backward (I  think) of the centre of the aircraft
P = 0^o pitch (firing on the same plane as the pitch of the aircraft)
H = -0.017^o ((I  believe) pointed slightly inwards towards the aircraft centreline)
B = 0^o bank ((I believe that) banking is not necessary for bullets or cannon shells (bombs aren't supported in Weapons for FSX)
QTY = 200 rounds of ammo (200 bullets)

So you will  need to mess with the Pitch, and Heading, to  get the bullets to head towards the Spitfire's Reflector Gunsite Reticle. It's a painstaking task, but in the end, satisfying to get the result you desire. I put in many hours doing a Weapon for FSX mod for the Captain Sim C-130 X-perience's AC-130 Bofor, Howitzer, and Minigun, only to lose all of it in a HDD crash. I get so upset every time I think of redoing it, and the frustration has not allowedf me to redo it. Yeah. I quit on it, which is something that rarely happens (usually once I realize that I simply can't do something anymore).