OOp

So I'm trying to learn OOp. I learned about all the features (inheritance, polymorphism and so on). I have two simple questions:

When is it advisable to instantiate objects instead of just using static methods? I always seem to diverge to imperative programming using only very few OOp features.

Don't OOp programs need a lot more of memory and processing power?

Thanks!

>>23
Well, please, tell me what you think the best DE JURE example [of abstraction] would be, so I can better understand your use of the otherwise nonsensical DE-FACTO there.