Antifa (short for "anti-fascist") is a group of people who don't like racism or people who hate others because of their skin color, religion, or who they love (this is called bigotry). They are people who want everyone to be treated fairly no matter what they look like, where they come from, or what they believe in.
When Antifa sees someone being picked on or bullied because of their race, religion, or sexual orientation, they try to help them. Sometimes they protest or demonstrate against organizations, groups or individuals who promote hate, violence, and discrimination or support bigoted policies.
Antifa believes that violence is sometimes necessary to protect people who might be hurt by hateful groups like white supremacists, neo-nazis, homophobes, islamophobes or xenophobes. However, some people say that Antifa sometimes uses violence themselves, and that makes it hard to support everything they do.
Overall, Antifa wants everyone to be treated fairly and they don't want anyone to be bullied, hurt, or victims of hate crimes.