Sorry for the delayed response. I've been on here since last year. I got on for a computer science class in school. I've spent many, many hours working on my games, which is why they look like they do. If you work hard on your games, you can make them look good too.
First you need to download Greenfoot. Have you done that yet? You might need Java 6 first, but just follow the download instructions. Next you run the downloaded and installed Greenfoot program, and follow the tutorials that come with the program. Or use the tutorials here. If you need help on getting any of the tutorials started, just ask on here, and someone will answer your question.
Sure, I'll follow you.
When you load Greenfoot for the first time, it should load up the Wombats scenario. If not, try clicking on the "Scenario" tab on the top left corner of the screen, and roll over "open recent". It should give you several options, and if you haven't made a bunch of scenarios since you downloaded Greenfoot, the Wombat scenario should be there.
I hope that helps.