In addition to NikolaeVarius' link, here's the law itself:

https://www.law.cornell.edu/uscode/text/47/230

It's a quick read, it's not long, and it's actually reasonably clear what it does and does not do.

Ars Technica's got a good explainer, including bits on why the law was enacted and what a purported legal framework without it might look like:

https://arstechnica.com/tech-policy/2020/06/section-230-the-...