The fork should come with an owner's instruction sheet and Park Tools has a tutorial on fork installation here: http://www.parktool.com/repair/readhowto.asp?id=111

Assuming the steerer is carbon DO NOT use a star nut unless your manufacturer specifically provides a special one. Use an expansion plug to allow adjusting the headset preload.

One more thing: you can always cut the steerer shorter. You cannot cut it longer. Measure a bunch of times before you get out the hacksaw.