Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.In other words, the Constitution promises Americans that Congress won't prevent you from speaking freely, but there are still caveats to this. For example, you can't yell "fire" in a public place when there is no danger. You also can't use "fighting words" or threats. This has been upheld by the courts repeatedly. You can be charged with a crime if you call someone a name and you can face legal consequences for it. There's more information on the exceptions to the First Amendment here: https://www.fas.org/sgp/crs/misc/95-815.pdf.