Javascript has me lost

Hello,
I am currently in a Javascript class and it is completely confusing me. I have a website that i am trying to make the tabs at the top all work. I have found lots of other websites that have good advice but they want me to do things way different than the book. Basically they are leaning me away from Javascript. The whole point of the class. I have included scanned pages of the book with the full description of the case problem. Can someone please take a look at these files and see if they can figure this out? I am including the original files as well as what i have so far.