You can find the playground here.
The Playground will be improved from time to time, so new features will be ready to be tested in the Playground as well.
You should also get in touch with OAuth. The Playground should guide you the way when and how using OAuth correctly. You can use your own credentials for authentication to see what the Playground is producing (provides header information) and what you get when using OAuth for your application.
How to use
You can start using the Playground with no further installation or knowing the API. On the left site of the page you have a small OAuth dialog and a request dialog. You can start a search without using OAuth. Just click and type in some attributes, e.g. region search with region id 003, and click on button Build Request. On the right top you will see the constructed URL. You can change the URL parameters and the click Execute. If there are no errors you will see a result.
You can change the representation format as well as the request method. In the documentation you will find some sample POST request you can use in the Playground. You can change the content type of the request body as well.
For some request you will need to authenticate using OAuth. The Playground uses standard IS24 test credentials, but you can use your own credentials. For example to add an entry to the shortlist you will need to be authenticated and logged in using three-legged OAuth.
If there are errors a useful message will be displayed.
In the Tutorials section you will find a lot more information and some useful guides.
There is only one thing you have to do now. Play around with the Playground to get a feeling of what the API is offering to you and your idea/ business needs around the API.