Which adobe photoshop to download?

I'm on here right now http://www.adobe.com/support/downloads/product.jsp?product=39&platform=Macintosh and I'm buying the adobe for my mac but I can't tell which one i should get. Do you have to download a main one and then buy extra features or can I get the most recently updated one?
Update: Oh wait I'm also a beginner, can you tell me which one is the basic one?
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