You're doing a garter stitch... knit every row (or purl every row). This stitch pattern creates a fabric that looks the same on both sides. That's why both your purls and knits look the same.
Here's a little practice for you. Cast on oh about 20 stitches. Knit one row, Purl the next. Repeat for 5 to 8 inches.
You'll soon see the difference between your purls and knits. The side that you knit on will be smooth and the stitches will look like little "V"s. On the purl side, it will be bumpy and the stitches will look like little bumps.