To learn what the difference is between a knit stitch and a purl stitch, you just have to remember that they are two parts of the same movement. They both just position the yarn on different sides of the fabric to create different looking stitches. One side of the fabric makes a V. The other side of the fabric makes a bump. Once you recognize those two shapes, you can read patterns much easier and just knit what you see on the page.
The working yarn should be held in back of the needles when doing a knit stitch. The needle inserts from front to back through the front of the loop on the left needle, you wrap it around, and pull it through to the front. This makes a V shape that you see knit stitches form in vertical columns. You can see more smooth V shapes on the face of the knitting in stockinette, and you see the ridge in garter.
The working yarn comes to the front of the needles before you make a purl stitch. You can enter the stitch in the back or the front, wrap the yarn in front and pull the new stitch off the needle toward you. At first, it feels weird to wrap the yarn in front to pull a stitch back toward you, but it works! This creates a little bump, which you can see on the wrong side of stockinette, and all the way down in garter. This is what you want for rib, seed, and all the other patterns you knit.
You can practice this with a smooth, light colored swatch. Make a small flat piece, and then make another swatch where you knit for a few rows and purl for a few rows. Don’t worry about making the swatch even on all sides, just look at how the two stitches are different. Feel the fabric with your finger. The flat knit stitches are easier to feel. This makes your hands and eyes learn how to recognize the patterns together, and soon you will know how they look without even touching them.
The most confusing part about learning knit stitches and purl stitches is knowing where the working yarn should be in the stitch. If the yarn is in the back when you try to purl, or in the front when you try to knit, you will make an extra loop on the needle. This is the kind of mistake that looks normal the next row, but your knitting gets bigger and bigger, row by row. Just always ask yourself, where is the yarn? Knit is in the back, purl is in the front.
This is why it is important to use stitch pattern abbreviations, such as K2, P2. This is telling you to knit two stitches, purl two stitches, which means you can see the ribbing pattern in the front and back. But if you don’t, look at the next stitch. Knit stitches are V’s, purl stitches are bumps. You just follow that pattern and continue.
As you knit more you may realize that the pattern is telling you two different things on different rows, like knit three and purl three on odd and then different on even. If you keep that up, you make a smooth stockinette swatch that is easier to make with fewer stitches in your hands. The progress that you feel with each knitting pattern is small, but every time you knit more you just knit a tiny bit easier, like counting less rows, or fewer accidental extra stitches in garter. It’s small steps, like checking how the yarn moves from back to front or front to back when you knit and purl. Just take a pause, watch where the yarn needs to move, and continue the stitches. That is how the pattern will read easier as your knit and purl skills grow.