okay, this is pretty simple. first make sure that you sew the seam that goes from the shoulder the the opening for the collar. (you can sew up the rest of the sweater now or save it for later, it doesnt matter) then with your circular needle, pick up (there's a very good video on knittinghelp) stitches around the collar. Just take your needle and insert it into the collar from the right side to the wrong side and pull a loop of yarn through (just like a knit stitch) and you repeat this step until you have the correct number of stitches. then you work all of the stitches in the circular needle in rounds (do not turn your work) just as the pattern says, bind off, weave in your ends... that's it.
I can't wait to see it