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!

This is a better discussion than half the shit on the front page, and that's unfortunate.
>>24
The best de jure example of abstraction is probably programming languages themselves. Experts determine the best way to execute code for some arbitrary set of constraints and then provide the means to turn an arbitrary set of syntax elements into the executable code, allowing developers to better handle their problem.