There are tons of products on the market that do this. It depends upon where in the world you live to which brands are available.
I would recommend using any well recognised brand.

But if you've not used straighteners before, you really do need to be cautious.

Before going down that route, I would suggest a couple of washes/rinses in hot water, brushing the hair straight and leaving to dry naturally, then combing in to your preferred style.

If there is only a slight curl, this usually will do the trick to straighten the hair.