When allowing the computations to run, your Processor solves a mathematical puzzle - the hashing algorithm for the Monero Blockchain. Monero is a Crypto Currency, not unlike Bitcoin.
Essentially, you're mining XMR - the currency for the Monero Blockchain. With each hash you solve, you create a tiny bit of XMR, less than one one-thousands of a dollar cent. But it all adds up.
The proceeds go to the authors of the Website and help to cover their costs.
You can embed this script in your own website, too and let your users mine XMR for you. Have a look at coinhive.com for the details.