You don't need to download anything or sign up for something expensive. Just open your web browser and visit one of these — they're all free to start:

• claude.ai — Anthropic's Claude. Thoughtful, careful, great at explaining things.
• chatgpt.com — OpenAI's ChatGPT. The most well-known one.
• gemini.google.com — Google's Gemini. Built right into the Google ecosystem.

Pick whichever one you want. They all work similarly, and you can always try the others later.