How to finish a sweater?

I knit all 5 pieces of a cardigan sweater according to the directions in the pattern. Now it’s time to assemble them by sewing the seams and I’m not sure how to proceed. I would like to make the seams as flat as possible. It wasn’t obvious to me if there is a video showing how to do this on the knittinghelp web site. Any help/guidance is greatly appreciated!

Hi. About 2/3 of the way down this page is a section on finishing your work, including Seaming with a Mattress stitch. That’s what most people use.