Perhaps one of the most daunting aspects of photography is learning how to play with all the features one can find on a SLR/DSLR camera.
And most likely, the case with not being able to understand how shutter speed or aperture modes work, or ISO and etc. is not because you don't want to learn how to use it, but it's just that you don't own a camera that you can practice with!
So, this is the next best thing I'll offer: a DSLR camera simulator that allows you to fiddle with the various settings of the camera and witness the results of such a setting.
Of course the picture is fixed and is in no way better than learning from a real thing, but this I believe is a good introduction for me, or anyone who would like to just understand the functions on the SLR.
But with all that said, having any camera is as good as any because like we learned in photography class - shooting anything with whatever resources you have is better than nothing.