Doing one in the round is all knit. Doing one flat is knit and purl and that’s all the stitches there are in knitting anyway. You would need to learn to decrease, but that’s just knitting 2 sts together.
Go look at knittingpatterncentral.com - lots of hat patterns. Making one in the round is on circular needles, so you may not be ready for that yet. I think Jan has a link to a hat pattern that’s knit flat. Basically, if it’s for an adult, CO enough stitches for about 20-22", knit in 2x2 ribbing for an inch or two, then you can continue in ribbing or knit in stockinette, start decreasing after about 8 or 9 inches and when you get down to about 10 sts or so, cut the yarn, leaving about a 12" tail, pull that through the remaining sts and seam up the 2 edges.