Open the playground with the link above. You will be presented with a splited window on which on the right hand side you will see the coding area, and on the right hand side the result area.
Currently there is a Hello World message with a lightgreen background.
Add a new variable message2 and greet with it the Galaxy.
Change the background colour to red.
Execute the changes by bushing the RUN-Button.
Check the result.
Your result is supposed to look like the following image: