When I buy ethereum -- what exactly am I buying?

[gomotomoto]

I've wrapped my head around bitcoin, but I'm spinning a bit when it comes to ethereum. Can someone help explain this to me?

To elaboarate...

I'm reading that ethereum is going to be used for multiple applications -- does that mean every time it's used (in any application) it lends to the mining of it's value?

If that's the case, isn't the upside for it surpass bitcoin?