I realize this post's title seems like it should be more descriptive, but we are talking about the knit stitch. It's usually the first stitch you learn when you learn to knit and it can be used in pretty much every way imaginable. Here are the most basic examples.
When you knit the knit stitch on both sides of your work, you get garter stitch like these dishcloths:
When you knit the knit stitch on one side of your work and purl on the other side, you're knitting the stockinette stitch like this dishcloth dress
. See how only the knit stitches are showing?
And when you work the knit stitch in the round, you have knit stitches on one side and purl stitch bumps on the other side of your work even though you're only working one side, like with this hat
And when you're learning to knit the stitch stitch, it looks like this: