I virtually guarantee you don't really understand how the regular monetary system works either, but you can still use it and have some idea of how it benefits you. Ethereum can be used to set up another monetary system whose currency flows are guarded by code-driven contracts that anyone can write.
So imagine the e-bay auction process as a smart contract that's controlled directly by the monetary framework, without involving Paypal or credit card companies, or any other centrally managed financial institutions.
The core idea behind Ethereum is sound and first envisioned a long time ago , but the current implementation leaves a lot to be desired. The Ethereum languages are being designed by programmers who try to address the needs one encounters in programming, like delegation patterns and some types of dynamism that makes extension and reuse easier.
Unfortunately, this is often the opposite of what you want for robust contracts, where writing the contract is not the important part, it's understanding all of the possible outcomes and what causes them. The dynamism makes static analysis hard, so understanding the behaviour of the complete system is too difficult, and vulnerabilities proving this point will continue to crop up.
Anyone can write a contract, but only a handful of people seem to be able to write correct contracts. And an incorrect contract means your money is gone.
If they had started with something like Nick Szabo's smart contract language, which is declarative, temporal and reactive, this would make smart contracts more intuitive and easier to get right. This sort of programming language has been empirically verified to be easier for most people to grasp.