This questions is too broad. Do you expect us to write the code for you ? It would be better to explain what attempts you have made to write the custom rating system yourself and the problems you are having.
Otherwise google Wordpress Post Rating system - find a plugin and install it.
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
This questions is too broad. Do you expect us to write the code for you ? It would be better to explain what attempts you have made to write the custom rating system yourself and the problems you are having.
Otherwise google Wordpress Post Rating system - find a plugin and install it.