Their homepage, if you scroll a bit down, has a fairly good explanation:

"""

What is Val Town?

Val Town is a social website to write and run code.

Vals are small JavaScript or TypeScript snippets of code, written in the browser and run in our servers.

Create scheduled functions, email yourself, and persist small pieces of data — all from the browser.

"""

So Val town is basically AWS Lambda. That still doesn't give me a good explanation of a "val". I'm guessing they don't want to use an AWS trademark but when I loaded the page I got a nice big table of prices and no useful definition of a "val".

While you describe the technical approach, I think OP was asking "what is it? What does it do? Why would I care?"

I can't really figure out the "Why would I care?" part from their website. I've been hearing them pop up a bunch. Just don't understand what they do.