Online chatting allows users to have conversations in real time through computer programs. It works using chat servers that connect users' chat clients, allowing typed messages to be sent and received simultaneously. The presentation discusses synchronous and asynchronous chat, with synchronous chat enabling multiple users to communicate at once in an online room. It describes chat clients, servers, and different types of synchronous chat like web-based chat rooms and Internet Relay Chat (IRC). Advantages include easy, quick communication while disadvantages include discussions becoming difficult with many users and chats not always being saveable.