I have a bootable USB with windows 8.1 on it. How do I use it to install windows 8.1 on my mac book pro 2013?

I created a bootable USB with windows 8.1 on it using a different computer ( a friend's macbook that had a dvd drive, mine does not).

Now that I have the bootable USB I want to install it on my macbook pro 2013. I can't find step by step instruction on how to do it.

Also I'm new at using a macbook so I'm reluctant to mess around and f...k things up.