The first step is to make the stencil. I have a video showing how I made mine- https://www.youtube.com/watch?v=XjbIsJbfNbo
Essentially what you'll need to do is tape one hexagon to the wall, tape around it, remove it and retape it, tape around that one and keep on repeating until the wall is covered.

Occasionally it helps to stop and make sure everything is lining up, level, and looks "right."

For an ombre effect, mix the main color with white (or white/grey/black to lighten and change the color). Start on one end and work the darker/lighter colors more on the other end.
It's really quite easy! For all the details and pictures, stop by the blog post!e