Telegram is a popular social app, and like most messaging apps, it has groups you can join. A Telegram group is basically like a big chat room. Users worldwide might be a part of a Telegram group, and you can either chat in real-time or reply to messages after the fact as you see fit.
Some channels function more like newsletters. In these, you cannot reply or chat with anyone. Instead, you’ll see a long chain of messages. That’s good if you want a big list of links and resources relevant to your interests that gets updated frequently.