Hats are slightly more complicated if you want a nice round bit at the top, but not so much that you really need a pattern for them either. If you've done a little knitting, and know how to knit, purl, cast on, etc., a patternless hat is well within your skill level. A bit of math and a swatch, and you're golden. Here's how.
Step 1: Tools & Materials
Depending on the particulars of your yarn, you will almost certainly need just one ball. Check the yardage on the ball so you know whether you need to adjust your calculations. My yarn came in balls of 100 meters.