Don't Understand Pattern

I’m very new at knitting and I’m trying to complete a sweater pattern that is knitted in pieces. I knitted everything but I don’t understand the instructions on sewing it together The pattern says:

Sew shoulder seams from armhole edge towards center for 2 1/2 in. [6.5 cm], leaving remaining edges open.
Mark 4 in. [10cm] down from shoulder on Front and Back. Sew Sleeve to between marks. Sew side and Sleeve seams. Weave in ends.
At neck edge, fold corner down 2 in. [5 cm] and tack in place. Repeat on the other side.

Could someone explain this please?

Looking at the picture may help in putting the sweater together and especially in shaping the collar.
Line up the fronts and the back with the right sides (public sides) facing each other and pin the shoulder seams together with safety pins or clips. Sew the shoulder seam starting at the armhole edge and working toward the neck for 2 1/2 inches. The rest of the fronts should hang loosely and not be attached at the shoulder seam because they form the collar. Now open up the sweater and lay it flat with the public side up. Measure 4 inches on either side of the shoulder seam and line up the top of the sleeve along these 8 inches (public sides of the pieces together), pin it in place and check to make sure it’s correct and that it fits you at the armhole. Once the sleeves are sewn in you can sew the sleeve-side seam in one long seam.
The collar can either hang loosely or you can attach it to the front with a few invisible stitches to hold it in place. The pattern suggests folding the corner over at the 2 inch mark (measured in from the neck edge) but see what seems comfortable to you. Enjoy wearing your sweater!