The two stitches just mirror one another. As you're going down a row, if you "knit" a stitch, you place a bump of yarn on the side facing away from you. If you "purl" the same stitch, the bump goes in the front, on the side you can see. These little bumps and indentations, done in a particular order, will create a pattern.
Garter Stitch is made by knitting every row:
Stockinette Stitch is made by knitting one row and purling the next, alternating throughout the fabric:
Seed Stitch is made by alternating your stitches - knit one, purl one - across a row and then doing the opposite on the next row - purl one, knit one - then repeating these two rows throughout the fabric.
Moss Stitch is made by alternating your stitches - knit one, purl one - across a row, repeating this for the second row then reversing the stitch pattern - purl one, knit one - across rows 3 and 4. Then repeating these four rows throughout the fabric.
It's deceptively simple.
Every knitter has their favorite patterns, and I'm no exception. For me, moss and seed stitch are very appealing. I recently started doing eyelets which requires making "holes" in your pattern by knitting two stitches together. Also, one of my crafty resolutions for this year was to do my first cable project - like the cables you see on sweaters. This is a very interesting technique that requires taking stitches off your needles and picking them up again later to place them "over" the other stitches.
When I attended the Crafting for Democracy at the Madison Capitol building, I made friends with a lovely woman named Colleen. She was knitting a pattern I'd never seen before and that I instantly fell in love with. For some reason, this pattern really sang to me.
"Colleen's Pattern" is a four row sequence. Row one - knit all the way across the row. Row two - knit one, slip one (slip the stitch, without knitting or purling it, to your right-hand needle) all the way across the row. Row three - knit all the way across the row. Row four - slip one, knit one all the way across the row. Then, of course, you repeat this four-row sequence throughout the fabric.
And this is what you get:
The best part of this pattern, in my opinion, is that both sides are pretty - even though the one side is supposed to be the "wrong" side.
Right now, I'm just making a scarf but I'll probably make something more impressive with this pattern at some point. It's just so gorgeous. If I do, you can bet you'll be seeing pictures of it here.