This braid is a part of a 3 part progression, so check this post out for the basic technique, and then this post for more clarification:)
Here is the tutorial in a nutshell……
To get the look, part off the top section of your hair in a half circle from one temple to the other. Thoroughly brush out the tangles.
Now, split the top section into 3 equal sized sections of hair, as if you were going to braid it. Clip off the outside sections so you can easily access the center section. Do a Ribcage Braid down this center section, dropping bits of hair every time you overlap.
Braid halfway to the ends of the hair, then secure the braid with an elastic or a bobby pin so it doesn’t un-ravel.
Now, begin a braid in the second section, beside your first braid. Overlap 3 times, and then begin adding in the dropped sections from your first Ribcage Braid. You will be adding the sections in to the inner side of your braid only, so every OTHER overlap. Continue braiding and adding in your first braid’s dropped sections. Continue braiding halfway down the to the ends.
Now with your final section of hair, begin a 3rd braid, and start adding in the dropped sections from the other side of the first braid, in the same manner as the second braid. Continue braiding and adding, halfway to the ends.
Now gather the ends of your 3 conjoined braids in the back of your head, and pin them together with bobbyy pins, in some kind of cool way like the one show, or you can check this post for more inspired bobby pin geometry.