Yes, you're knitting garter stitch.
One thing to understand is that the front of a stitch is the knit and the back of the stitch is the purl. It's one stitch, each side has a name. When you knit every row, garter stitch, the purl side goes on the back. When you turn it around and knit the other side, the purl side goes on the other side.
When you knit in stockinette, which is what most sweaters, for example, are made with, you knit the 'right side'--the side people see, and your purl the wrong side, or inside.
So if you knit one row and then purl one row, stockinette stitch, you get all the knit part of the stitches on one side and all the purl side of the stitches on the other side.