If you're knitting in the round, dpns or circulars are what you need. If you are knitting flat then seaming, you can use any needles you want. Do you have a particular pattern in mind? If so, a link to it would be helpful.
You can use any method you want. If you don't mind seams then straight needles are fine. I prefer seamless myself.
There are several methods of knitting in the round if you choose to do so. Magic loop with one long circular needle, two circular needles or DPNs. There are videos for all of these in the video section above.
What size hat are you making? Do you have a pattern?
Looks like this can be knit in the round or knit flat. Many people said it came out too small so make sure to measure and figure out how many sts per inch so you know if it'll fit you or someone you know.