You will need a wide tooth comb, clear elastics, and bobby pins if your layers are a pain.
Step One: Put your hair in a pony using an elastic on the side you want your braid on. Comb out your hair, if you want an extremely messy look don't comb it out, if you want a neat look, do this right out of the shower.
Step Two: Separate your hair into two pieces and hold one in each hand.
The rest of it:
What you will do is take small to medium (depending on your hair type) from the back of one side of hair and bring it to the front and give it to the other side, repeat that process alternating and crossing over. I included a video of me in the process. No judgement that it is not a bueno video.
After you are done, take the elastic and carefully cut it with a pair of scissors so that you have a loose braid and you will have a finished product that looks like:
Well this is a messy version of it!
After you have it, you can gently pull the sides apart a little and it will look a lot chunkier.