The people have the right to "peaceably assemble."
Maybe you've seen some anti-war protesters, veterans, farm workers, immigrants, pro-life and pro-choice groups or consumers who are boycotting businesses.
A crowd chanting and carrying signs can have a powerful effect on public opinion, the media and lawmakers.
Notice the word "peaceably."
When a crowd gets out of hand it becomes a mob. The safety of bystanders can be threatened and the police have a duty to maintain order and safety. Citizens aren't free to block streets or destroy private property. That's a no-no.
Authorities can require permits for large gatherings. But the Supreme Court has ruled they can't be used as an excuse to silence protests.
There's a similar right that's not named in the Constitution. Courts have ruled that the "freedom of association" allows you to be a member of all kinds of organizations and groups and the government can't mess with you. So the Bob Marley Fan Club that meets in your garage - no problem, mon.