Use a de tangle spray. Johnson's makes a good one.
start at the points of the hair and work backwards towards the roots
use some detangling spray.
start at the points of the hair and work backwards up the hair towards the root. this reduces damage and tearing to the hair.
If you are asking about hair that is gnarled and tangled upon your head, most conditioners or hair-use oils will help to get the job done and the use of a comb or pick will help even more.