What is an LLM?
LLM = Large Language Model
It's a program trained on millions of texts that can understand and generate human language. Including code.
The key insight: An LLM can write code for you. You just have to ask properly.
The "Prompt-First" concept
Instead of memorizing syntax and copying code from Stack Overflow, you can:
- Describe what you want in natural language
- Ask the LLM to write the code
- Run the code it gives you
- Iterate if something doesn't work
This works with any LLM: Gemini, ChatGPT, Claude, etc.
Where can I use an LLM?
| Option | Access | Cost | Ideal for |
|---|---|---|---|
| Google AI Studio | Google account | Free | Getting started |
| ChatGPT | OpenAI account | Free/Paid | General use |
| Claude.ai | Anthropic account | Free/Paid | Code and reasoning |
| Ollama | Your computer | Free | Total privacy |
💡 Recommendation: Start with Google AI Studio. It's free, no credit card, and you already have an account.
Main LLMs (2026)
| Model | Company | Strength |
|---|---|---|
| Gemini | Free, multimodal, easy API | |
| Claude | Anthropic | Excellent for code, reasoning |
| GPT-4 | OpenAI | Versatile, broad knowledge |
| Llama | Meta | Open source, runs locally |
What is an API Key?
When you use an LLM from your code (not from the web chat), you need an API Key.
It's like a password that identifies who is using the service.
| Service | Where to get it |
|---|---|
| Gemini | aistudio.google.com/apikey |
| Claude | console.anthropic.com |
| OpenAI | platform.openai.com/api-keys |
⚠️ Never share your API Key or upload it to GitHub.
Key concepts
| Concept | What it is | Example |
|---|---|---|
| Prompt | What you ask the model | "Write a chatbot in Node.js" |
| Response | What the model answers | The code + explanation |
| Token | Unit of text (~4 characters) | "Hello" = 1 token |
| Context | What the model "remembers" | Previous conversation |
Practice
→ Chatbot with Gemini — Your first AI project