My Back Glass is shattered. How can I fix that myself?

This looks like a good video on how to do it!
You just need a bunch of heat and some Xacto knives :)
But make sure to disassemble the phone all the way first like they do in the video, otherwise stuff inside will probably get ruined.
When buying new glass for it, you have to make sure you get an aftermarket piece with a slightly oversize camera section, since the glass normally goes under the edges of the camera bump, and then it is permanently welded in place from the back.