There are two ways by which you could acquire the dreadlocks hairstyles for your hair. The simpler but longer way of acquiring such a hairstyle is to go the natural way, of letting your hair go. All you have to do is keep your hair messed up, do not comb or brush it and tie as many knots as you can in the hair. Of course if you are not going to wash it at all it would eventually start to smell and itch, but either you rough it out to keep that look or you could mildly clean it. But this method surely takes longer.
You could also artificially create the dreadlocks hairstyle for yourself. You would need the special kind of dread wax that is required to acquire the dreadlocks hairstyle artificially. Besides this you would need a metal comb and some shampoo, also you will need to tie some knots so some rubber bands for that.