Well if you want to create crux art, I would suggest that you start with Daz Studio. It's a free download (though a lot of the content is not - although this is the internet, so everything is free if you know where to look for it
and there is a fair bit of genuinely free content for it out there too) and is pretty stable. For best results, run it in native Windows 7 - I have a Win7 PC just for doing 3D art - mt main system runs Linux and while it is possible to run Daz under Linux with a fair bit of messing around, I've never been able to get it to run as nicely as it does in windows 7
Daz is fairly easy to use once you get to grips with it, but it does have a steep learning curve. Fortunately there are thousands of great tutorials on Youtube and elsewhere on the internet.
If you want to do 2D photo manipulations rather than actual 3D art, then Photoshop or one of the free alternatives such as the amusingly (and appropriately) named GIMP will be the way to go. In this case almost any painting software will work, but you really need one that supports layered editing (so MS Paint is out as far as this is concerned)