Does anyone here have experience with SSP Applications?

I've done a lot with standalone SSP, but nothing in conjunction with SCA.

I was told to ask here. Right now I’m just trying something super basic - just a Hello World HTML page. But instead of displaying, it just tries to download itself when I go to the URL.

The URL is probably wrong - the link shown in the file edit window in Netsuite is incorrect. You should use web root URL + SSP URL root + filename

I don’t think so - it’s finding the right file. It’s just that the browser doesn’t render it as HTML, it tries to download instead.

Assuming it's just a "Hello world", you're welcome to DM me a link if you want and I can see if the URL appears correct.