It's not all that difficult. the first thing you need to do is cut your trimmers. The trimmers should be cut at the height of your headder bottom. Mount your king studs to your trimmers, make sure that the wane is facing the center of the boards and the crown goes the same way. 2 nails on the top and 2 on the bottom with nails staggered every 16" all the way up. Next cut your header. It will need to be 3" longer than your rough opening to sit on your trimmers and nail thru your king studs. Now find your rough opening height, subtract it from your trimmer height and subrtact 3". Now cut your cripples. They will mount to either trimmer, opposite your king stud and every 16" or 24" to match your stud layout. Finally install your sills over the top of your cripples. Some things to keep in mind: King studs are continuous from top plate to bottom plate. Header's are generally the same height. The longer the window the thicker the header. Luck, Gerald