With the amp you're getting i doubt there will be a difference in sound when changing pickup positions
Decent amp + decent pickups = significant change in sound when changing pickup position
Poor amp + poor pickups = very subtle change.
There are three positions
Bridge,middle and neck pickups. The washburn you've purchased has a humbucker in the bridge position (closest to bridge) and two single coils.
Bridge is usually used for lead, neck (closest to neck) for rhythm and the middle for either splitting the two humbuckers or giving a nice twangy sound.
I must warn you though if you get in to guitar be prepared for GAS
I think I've spent around £3000 since last august on gear and i only work once a week
Have a custom lined up that is going to cost around £1500