http://www.howtogeek.com/120482/how-to-root-the-nexus-7-galaxy-nexus-or-nexus-s/ a guide how to do it.
once you have rooted get an app from google play called stickmount.
you will need a file browsing app like astro file manager.
then grab an otg cable from amazon (mine cost £1.50)
This was my first ever attempt at rooting anything,so if anyone can give me an suggestions i would greatly appreciate that!!