To use ChatGPT, start by creating a free OpenAI account on chat.openai.com or through the ChatGPT mobile app. Once logged in, you type your question or prompt into the message box and press Enter. ChatGPT will generate a response in a few seconds, and you can interact further by editing your prompt, asking follow-up questions, copying the response, or regenerating answers if needed. The interface also allows voice input, uploading files, and sharing conversations via a unique URL. If subscribed to a paid plan, you can choose different AI models or create customized GPT assistants with specific instructions for tailored responses. ChatGPT can be used for a wide range of tasks like answering questions, writing, research, and much more, making it a versatile AI conversational tool.