Curling with flat iron?

You can definitely achieve waves (experiment with your irons - basically just move them in a waving motion rather than the usual straightening one - it takes a bit of practice but you'll get the hang of it!)  You'll need to apply a serum to your wet hair to ensure that the curls don't go frizzy, plus your usual heat-protective product (try to find one that doesn't also contain a "straightening" agent as that will pull the curl out of your hair).

I'm not sure about actual curls, though; I've heard that it's possible, but I don't know how!  Maybe you could ask your stylist next time you have a haircut and even get them to show you?  Good luck.