The most versatile hair tool is the Flat Iron. It can be used to create different hair looks from sleek straight hair to curls it could all be created with this tool depending on how you use it. There are three types of flat irons:
The wide flat irons are made for salon use, mostly to seal the hair cuticle after chemical treatments like the keratin. These could be used also to style your hair straight.
The thinner irons (about 1.5 wide) are for styling, you can create almost every look with them depending on how you use them. Pass flat along your hair for a straight look, twist it along the way so you could create waves and curls.
Texturized irons are used to create waves and volume along the hair, they are only used by pressing the hair to create the texture.