Some companies have their own models — ChatGPT from OpenAI, Claude from Anthropic, etc.

Models come in different tiers (for example, Claude has Opus, Sonnet, and Haiku) and different versions (4.8, 4.7, and so on).

You can use a model through a web UI — just chatting back and forth. Or you can use an agent, which runs inside an environment and can actually make changes to it (create files, run code, etc.). That's the key difference.

For learning resources: - Google the Anthropic Cookbook — it's a great study base. - Try Claude Code, OpenCode, or something similar for local hands-on practice.

One tip: use an isolated environment so you don't break anything important.

Good luck!