I am not sure by what you mean by many different ones. There are two, photoshop and photoshop elements.
elements is about 5% of the cost of photoshop. of course it does less, but might well be enough for what you need.
Photoshop , the latest is CC, but you don't own that anymore you rent it every month. cs6 you can still buy however. If you do decide to buy an older version of photoshop then it comes in 2 flavours, normal and extended. The extended gives you 3d functionality ( if you need that )