Every post rides on top of a deep legal stack: a federal immunity statute, constitutional doctrine, copyright, advertising regulation, labor law, and a patchwork of privacy and promotions rules. This field guide takes the stack apart layer by layer, for the founder running a giveaway, the marketer running an influencer program, the manager tempted to fire someone over a Facebook post, and the official wondering whether blocking a critic is a constitutional problem. It works through Section 230 after Gonzalez, Taamneh, and Moody v. NetChoice; the state-action test of Lindke v. Freed; the FTC's endorsement rules and its 2024 fake-review rule; the National Labor Relations Act line around employee venting; state password-protection statutes; the unsettled ownership of a company account; and the everyday doctrines of defamation, anonymous-speech unmasking, impersonation, and lawful giveaways. Plain-language throughout, densely sourced, with invented worked examples and cross-links to deeper UpLaw resources. Not legal advice; consult counsel before you act.