The Constitution of the United States limits Congress from making laws to limit the freedom of speech of United States citizens.
So the Constitution prevents Congress from infringing your right to say things.
The Supreme Court has decided to give Congress a pass on this in certain instances.
Speech intended and likely to incite immediate lawless action is not protected. An example of this is the oft-cited shouting “Fire!” in a crowded theater when there is no fire. It is important to note that the specific flavor which the Supreme Court has allowed the government to proscribe is both immediate and illegal. Neither on its own is grounds for censorship.
Threatening someone. This does not extend to hyperbole: only to so called “true threats”. For example, expressing political opposition to a President such as “I am not going. If they ever make me carry a rifle the first man I want to get in my sights is L. B. J.” (Watts v. United States) would not qualify as a true threat.
Being obscene, specifically pornographic, is also not a form of protected speech. There are specific standards for this category, all of which must apply for the content of the speech to be unprotected. To paraphrase, the Miller test asks, “would an average person think of this as lustful; is it offensively sexual in nature as defined by state law; and does it lack literary, artistic, or scientific value?”
Humorously, the government can censor itself.
The protection of several other forms of speech are limited in some way. Libel and slander, speech by public employees pursuant to their official duties, student speech, and the clear-as-mud blanket “national security” are among these.
There is no mention made in the Constitution of anyone’s responsibility to care what you have to say. Nor is there any protection against retort. An argument I see often when people are not-so-kindly asked to keep their freedom of speech to themselves is that this is a free country. Usually on the Internet.
No protection in the Constitution prevents others from telling you that they don’t want to hear it anymore.