When the knitting is complete and it comes time to sew your sweater together, there are several different finishing techniques that can help give you a professional look. For joining the side seams of a sweater, the mattress stitch is an easy way to get a strong, invisible seam.
The mattress stitch is good anytime you want to join two stockinette pieces together. So while this stitch is one that you'll use time and time again when knitting a sweater, you'll also use it plenty of times with other projects.
Here's a quick tutorial knitting video on how to do seaming with the mattress stitch.
In this knitting video from www.KnittingHelp.com , Amy shows you how to create a beautiful invisible seam using mattress stitch. This knitting how-to video uses a contrasting color yarn so it's easy to follow along.