This is one of my all-time favorite braids, especially for the summer.
Just like a regular braid, you start out by taking three strands of hair--but instead of separating all of your hair into the three parts, simply take small sections: one directly in the middle and two sides.
Now, start to bring in more strands, adding more hair to both of the side strands as you go. But do NOT add hair to the strand that is in the middle.
Keep adding your hair as needed, continuing the braid as normal.
And there you go! It's as simple as that. You can either take smaller strands for a more detailed and tight braid, or you can take bigger sections (as seen in the photos), which will give the braid a looser feel.