Require is not defined
The "require" function is only available in the "bundle.js" script context. Browserify will take all the script files necessary and put them into the "bundle.js" file, so you should only have to include "bundle.js" in the HTML file, not the "script.js" file.
The idea behind Browserify is that you can split up your sources using CommonJS modules and bundle them into one file to be used in the browser. Browserify will traverse all your sources and will concatenate all required files into the bundle.