Welcome, nyy. Trying to keep it simple; the rudder is the control surface you use least in normal flight (in real life and on FS9 both). Turns are mostly achieved using banking. Just like a bike, really, at any kind of speed you turn mostly by leaning over. The rudder is mostly useful taxiing on the ground, and for keeping the aeroplane straight on the takeoff run.
The rudder is also useful for landing in crosswinds - but you can do without it by 'aiming off' (i.e. pointing the aeroplane's nose upwind of the runway line). Anyway, you won't have wind problems on FS9 until you start using 'real weather'.
There are two basic types of joystick - the simple two-axis one, and the more expensive 'force feedback' type. One or other of them is essential, flying by 'key control' in FS9 is just about impossible.
If you have a two-axis one, go into 'Settings', then 'Realism', and select 'Autorudder'. You will then find that, in flight, the game will automatically coordinate rudder with aileron movements. For taxiing and taking off, you can work the rudder by moving the stick sideways.
If you have a force-feedback one, you can still use 'Autorudder' when you're starting off. But if you turn 'Autorudder' off, twisting the stick works the rudder.
Rudder pedals would be nice for complete realism - but they're not essential.
The main thing, if you're starting out, is to GET FLYING. And start off by doing the first batch of lessons with Rod Machado (the Student Pilot' ones). They only take about five minutes each, and they are definitely the shortest way to get the basic hang of things. They'll get you off to a flying start, if you'll excuse the pun