From the Summary: "Section 230 of the Communications Act of 1934, enacted as part of the Communications Decency Act of 1996, provides limited federal immunity to providers and users of interactive computer services. The law generally precludes providers and users from being held liable--that is, legally responsible--for information provided by a third party, but does not prevent them from being held legally responsible for information that they have developed or for activities unrelated to third-party content. Courts have interpreted Section 230 to foreclose a wide variety of lawsuits and to preempt laws that would make providers and users liable for third-party content. For example, the law has been applied to protect online service providers like social media companies from lawsuits based on their decisions to transmit or take down user-generated content."
CRS Report for Congress, R46751
Congressional Research Service: https://crsreports.congress.gov/