This collection of files serves as a simple static demonstration of how to post to a google spreadsheet from an external html <form> following the example by Martin Hawksey
You should be able to just open index.html in your browser and test locally.
However if there are some permissions errors you can make a quick html server with python. Open terminal and cd to the directory where the gist files are located and enter python -m SimpleHTTPServer. By default this creates a local server at localhost:8000