If you know Smalltalk, you can write some programs here. It's basically a programming environment, with some operating system functions. You can edit Scratch Public Sources there.
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Well, the first step is downloading both the image and the VM. Did you do that?
Then you can open it. Click and hold on the background of the window that opens and a menu will pop up. Go to file>new morphic project (I'm not sure if it's exactly that, so if you don't find it there you ought to look around). Then you have a project. Click on it and it will expand to the whole screen. Then you should learn how to use Squeak using the famous BankAccount Tutorial.
Scratch on!
Coolstuff
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