To get straight hair I would suggest using a straightener. It is a iron to straighten hair :).
How can I get straight hair?
If your hair is very kinky and /or coarse,you may have to purchase synthetic hair and have it professionally attached to your natural hair. Otherwise,you should be able to use a straightening serum (such as John Frieda "Frizz Ease") applied and combed (not brushed) through towel dried hair. Follow that with a blow out using a round brush,then finish by applying a heat protecting spray and using a flat iron.
Well, when you dry your hair, you should use a brush and separate your hair Into sections while you dry it. Also, you should use a straightener to straighten your hair and set it to a good temperature for your hair. After you straighten it, you should brush your hair out so it stays nice and smooth :)
Straighten your hair.