To start playing, you should first choose a level – either click "Select Level" or hit the "s" key and the Level Selector window will pop up. Use the "n" and "p" keys to highlight the next and previous levels, respectively, or click one with your mouse. Then hit enter or click the "load" button to load the selected level. If the level has some help text, it will be displayed in a dialog after it has been loaded. As you complete levels, this will be indicated by a green checkmark on the level's thumbnail.
To debug your code, log diagnostic information to the console. You can view the console by clicking the arrow on the bottom of the screen or by hitting the "c" key. For more information, take a look at the logging functions.