Black hairstyles, especially long hairstyles like this are known as flat ironed with curl at the end.
To get this style it’s important to use a thermal protectant from mid-stand to end. Do not attempt to flat-iron with wet hair. A ceramic flat iron is recommended and should be set on medium to high temperature.
With the flat iron in hand, gently place a section of hair within the grasp of the flat iron. Squeezing gently, slide down the hair, starting at the roots and continuing down. Do this two times and at the end of each slide, curl inward with the flat iron.