Just like in Windows, Linux is designed for many users. Some users are like administrators with lots of power, called superusers, while most are regular users. Interestingly, not every user is a human - some are created by programs for added safety.
Then there’s groups. Think of groups as teams. Instead of giving permissions to each person, you can give it to a whole team. This way, if everyone on a team needs to access a certain file, you just give the team (or group) permission, not each person.