Reverse Coding in GSS, Brief Explanation Requested

I am doing a data analysis project in my statistics class and my professor liked all the data tables that I had found for my proposal and asked me to reverse code a few of them; however he for some reason will not explain how to reverse code and has even left a few other students scrambling (the text book is no help either). I have provided a link to the website we used to get the data from and a link to only one of the tables I am using. Will someone be able to provide a brief explanation on how to reverse code?

GSS site:

GSS data table: