Cloud 9 is the easiest way to start developing. It's gives you everything you need without the hassle of downloading Ruby on Rails and the various tools it requires. There are multiple tiers for Cloud9, but the free one will work for class. You can sign up at c9.io

In Cloud9, go to your settings by clicking the gear on the top right.

Select SSH Keys from the menu on the left side. Copy the key.

Now let's set up github. If you haven't already, visit github.com and create a free account.

Once your logged in, click on the top left icon Settings SSH keys Add SSH key

Enter a title you'll remember. Titles are a friendly way to identify which key is associated to a computer. If you replace your computer, you'll want to delete the key that is associated with it.

Paste your SSH Key and click Add Key!

Finally, sign up for a free account at Heroku.com