jQuery - 在多个div之间切换不起作用

I've found here, on Stackoverflow, function, which should toggle between multiple divs. I tried it in JSFiddle and it worked. But for me, on website, it doesn't work. I am really not good at javascript / jQuery, so I will be really glad for any help! And one more thing - is it possible to set link, that I just clicked on add class "active", that it would have underline or something, to see which section is selected?? Thanks! -- FIDDLE HERE: I've found here, on Stackoverflow, function, wh