Does what it says on the tin :)
The main script (main.js) relies on two lists of words called patterns.js, which is a stock of sentence patterns made up of fixed words and variable words, and vocab.js, which contains these variable words.
For example, take this sentence pattern from patterns.js:
This life is nothing short of a ing nOf of adj nMass
Here there are 4 variable words: ing, nOf, adj and nMass.
The script looks inside vocab.js for those 4 words. In the case of ing (a present participle), it might choose "flowering" or "unveiling." For nMass (a mass noun), it might choose "consciousness," "growth" or "stardust."
It then fills each heading and paragraph of the page with a certain number of sentence patterns. Paragraphs get three sentences each, for instance, while each heading gets one.
It avoids duplicate sentences by making a copy of the entire pattern array found in patterns.js at the start and removing each sentence as it is used.
The pretty picture comes from placeimg.com, which generates a random image each time something visits its URL.