Some Fundamentals  

It's easy for those of us who've been knitting for years to take all this for granted and harder to remember what it was like when we were new knitters who didn't yet know the difference between a knit and purl stitch... or between the "knit" that's a stitch, and the "knit" that refers generically to the activity we all find so addictive and that means "work some stitches" whether they're to be knitted or purled.

Because things always seems more understandable to me if I'm actually doing what's being described, than they are if I try to imaginesometing I don't understand in the first place, I'd like to suggest that you pick up your needles, cast on about fifteen stitches, andfollow along in a practical sort of way --

When you knit (activity), you take the stitch on the left needle off thatneedle and position its LOOP below a new stitch on the right needle.   KNIT stitches make the loop go away from you and form a bump on the back of your work.

PURL stitches make the loop come toward you and form a bump on the front of your work.

Knitting every stitch of every row gives you bumps on both sides of the work, and we call this GARTER STITCH. (Here's something to think about -- and try --PURLING every stitch of every row also gives you garter stitch.)

Alternating a knit row with a purl row gives you one flat side and one bumpy side; this is called STOCKINETTE STITCH.

Alternating knits and purls in the same row gives you many different pattern possibilities. Two of the most popular and useful are ribbing and seed stitch. Both are reversible, so they're good choices for scarves. (DON'T forget to move the yarn forward when you're going to purl and back again when you're going to knit!)

RIBBING is the result of working K1, P1 ( or K2, P2 ) across the row. In each row, the knit stitches line up with each other, creating columns of flat stitches, and the purls line up to make columns of bumps. (Of course, the bumpy column on this side is the flat column on the other side --have a look!)

SEED STITCH is just like ribbing, except the knit and purl stitches don't line up, but are offset, running on the diagonal. To make it, Knit the stitches that look like Purls, and Purl the stitches that look like Knits. Each knit stitch is in the middle of 4 purls, and every purl stitch is surrounded by knits.