How do you seam together a ribbed hat?

I’m a new knitter and I’m making a 2x2 ribbed hat on straight needles for my 3 month old daughter. I can’t seem to find any videos showing how to properly seam up the hat when I get finished knitting the pattern. Any help would be great!

Use mattress stitch.

There’s some good help here.
http://www.knittinghelp.com/videos/knitting-tips