2018-04-13#tokens (known as “Ether,” or ETH) on Ethereum, you are buying “work units” in a massive, cryptographically secure computer and cloud network spanning the entire globe.
Storing or changing data on the Ethereum blockchain costs ETH, but it is a one time cost. Retrieving the data is free, which is great for static content on web pages, like images. When a website hosts an image on the Ethereum blockchain, users can retrieve that image by pointing to its hash. Or rather, the website administrator would do this, and you as the user would have no idea. You would load the image from the Ethereum network in your browser without realizing it. It would look and act like a normal website, but underneath is a series of extremely complicated mathematics (aptly called mathemagic by the Ethereum Foundation) that make the most widely used encryption today look like crayon drawings.
So what about dynamic content? This is where Smart contracts come in. Developers can use Smart contracts to store memory or to “do something” on the blockchain. For example, imagine a (pretty awesome) website where users input a number, and the website computes and returns double that number. In this case, the website would send the submitted number to a smart contract that would store it in memory, then perform the doubling calculation and finally output the result. If the user wants to recall a calculation they made previously, or submits the same number as before, this can be done without needing to re-submit to the contract. All transaction history is permanently stored within the blockchain. You only have to calculate or “do the thing” once, and never have to waste precious CPU time again. You can simply recall the previous transaction and return its stored result. As more transactions are appended to the blockchain, computation becomes more efficient.