Before you can start coding your first client application, there are a few things you need to do, if you haven't done them already.
Get a Google Account
You need a Google Account in order to be given access to Google Compute Engine in the Google APIs Console. If you already have an account, then you're all set.
You may also want a separate Google Account for testing purposes.
Sign up for Google Compute Engine
If you don't have access to Google Compute Engine, sign up for the service.
Try Out Google Compute Engine
This API documentation assumes that you've used Google Compute Engine, and that you're familiar with web programming concepts and web data formats.
If you haven't used Google Compute Engine, then try out the Quickstart before starting to code.