They do often use straight needles for beginners, but there's no reason you can't learn on circulars. I use circular needles for nearly everything now.
You'll be knitting flat (not a tube of knitting) to learn so you will have to learn how to turn your work so you don't join into a tube. It's not hard though. Just remember that knitting is awkward for everyone at first so just start and keep going. Your tension and technique will improve with practice.