Ethereum is not a web hosting platform. It is not similar to Amazon's EC2 or anything like that. Conceptually, it is a single global computer that anyone can access. It's not the same kind of computer you're familiar with, though.
Programs on this computer can't be changed, and nothing can write to the program's storage except for the program itself. You don't have to trust a service provider to maintain their guarantees: it is impossible to break a guarantee.
These characteristics are useful for writing programs that coordinate interactions between humans. They're also useful for letting devices publish and access information about the world long after their manufacturers go out of business.
Entirely new kinds of software can be built to coordinate social and financial systems.
