This site is built using Notion (What's Notion?), and made possible because via Notion you can share pages/notes to the public via a URL. As such, every page you create in Notion has a unique URL: this consists of the title of the page plus a random hash (collection of letters and numbers) appended to the end because page titles aren't necessarily unique.

So that's why some URLs look a little "messy".

As for why some others look "clean" - that a feature of Fruition (What's Fruition?) called "Pretty Links", where you can map individual "messy" URLs to cleaner ones. I've done this for some pages (like top-level ones), but not all of them (like blog posts) - so that's why there's a mix.

Check out the above linked pages, or About this Website to learn more.