New knitters often have trouble once they learn how to knit and purl, understanding the difference in looks between knit and purl stitches on the needles. Knowing how to "read your knitting" is important because it will allow you to find mistakes in stitch patterns and know how to fix them.
The Difference Between a Knit Stitch and Purl Stitch
The most basic thing to know when learning to read your knitting is the difference between a knit stitch and a purl stitch.
Most knitters learn the knit stitch first, and they are used to seeing the bumpy ridges of garter stitch that are formed by knitting every stitch on every row.
Once you throw purling into the mix, things can get a little more confusing. Now you see that the "bumps" are really purls, and that knitting and purling are two sides of the same coin—or the same knit fabric.
Looking at the sample of ribbing pictured above, you'll see columns of Vs and columns of bumps. The Vs, or flatter-looking parts of the fabric, are knit stitches, while the bumpier sections are purls on the right side.
That "on the right side" is important, because on the back side of the knitting you knit the opposite stitch to produce the same look on the right side—the back of a purl looks like a knit stitch and the back of a knit stitch looks like a purl stitch.
This is why patterns will sometimes tell you to "knit the knits and purl the purls" as you see them; you're not repeating the previous row but doing the opposite so that the two rows look the same on the front side of the knitting.
When looking at the stitches on the needles, too, you can see the difference between a knit stitch and a purl stitch: the knit stitches are plain loops while the purls have that little bump (or "pearl") underneath.
Once you understand what knit and purl stitches look like, it's a lot easier for you to find mistakes in knitting stitch patterns as you're working. If you know what two knit stitches followed by two purl stitches are supposed to look like, both in the knit fabric and on your needle, then you'll see mistakes in that pattern more easily.
For example, in this photograph, you'd be able to see that there's an extra purl stitch. The stitch in the middle of the picture is a purl that should be a knit. You can see the extra bump on the needle as well as in the knit fabric—there's a bump where it should be smooth.
Watch Now: How to Pick Up a Dropped Stitch
Once you see the problem, what can you do about it? If you're on the same row where the mistake occurred, you can "tink" (that's knit backward) the row, carefully placing the left-handed needle through the stitch on the row below then pulling out the stitch from the current row until you get back to the mistake.
If you notice the mistake rows later, you can intentionally drop a stitch after knitting over to the stitch with the mistake. Drop the stitch down to the row before the mistake and use a crochet hook to pick the stitch back up, either as a knit or a purl depending on where you are in your pattern.