twentyfifteen implementation

Hi, for me the instructions on this page do not work (https://vip.wordpress.com/documentation/incorporate-co-authors-plus-template-tags-into-your-theme/). I have no other plugins installed, its a very simple text blog with twentyfifteen theme.

Can anyone just give a list of the pages and the code I need on each page in order for the plugin to work with twentyfifteen theme?

I would really appreciate it because I have been trying lots of forums and nothing seams to work. I have very limited knowledge of php.