What “training” actually means
A language model is the program behind ChatGPT and every other assistant: it learned to write by reading enormous amounts of text (we cover it in what an LLM is). Training it means changing it from the inside so it behaves differently. That's an engineering job.
People who search for how to train AI on company data almost always want something else: answers that use their rates, their products and their rules. You get that by putting the paperwork in front of it. There are three paths, and only the third one is training.
The key idea: you don't teach AI about your business by changing it from the inside. You put the documents in front of it and, when a fact changes, you change the document.
Path 1: paste the information into the conversation
It's what you already do without a name for it: you copy some text or attach a file and ask. What you type in that box is called a prompt: the request plus everything that goes with it.
When it works: for a one-off question with a few papers. The owner of Three Gables Creamery attaches the labeling rules and asks whether her new label meets them.
Its limits: you have to repeat it in every conversation, each person pastes their own version, and only so much text fits. For five PDFs it's fine. For the whole company it falls short.
Path 2: give it documents it looks up before answering
Here the documents are uploaded once to a shared place, and the assistant searches them every time somebody asks. The technique is called RAG, “retrieval-augmented generation”: before writing, it retrieves the pieces of your documents that apply and answers with them in front of it. The set of documents is called a knowledge base.
- You update it by changing the document. If Three Gables raises the price of its aged cheddar in January, it swaps the price list and that's it.
- It can show the source. Because the answer comes from a specific document, a good tool lets you open it and check.
OpenAI frames it the same way in its developer guide: when the model is missing information, or has it out of date, you retrieve it from your documents. Retraining is for something else.
Path 3: retrain the model
This one is training. It's called fine-tuning: you give the model many examples of a question and a well-done answer so it learns a behavior, like a very rigid format or a way of reasoning.
Per that same guide, it fixes problems of behavior and consistency, not of knowledge. You have to prepare the examples, have someone technical on hand, and do it again when something changes. And a retrained model can't show which document a fact comes from, because it doesn't come from any.
When it makes sense: in a program that does the same task thousands of times and needs an exact format. In a small business that wants its assistant to know the place, almost never.
How to train ChatGPT on your own data: upload it
If what you were looking for was how to train ChatGPT on your own data, in practice that means uploading your files to it. There are two ways:
- In a conversation. Click the “+” button in the message box and choose to add photos and files. It takes the usual office formats, with limits on size and number of uploads that depend on the plan.
- In a project. A project keeps files and instructions that apply to all of its conversations: it's path 2 inside ChatGPT. How many files fit depends on the plan.
We don't give figures because they change often; today's are in OpenAI's help article on uploading files and in the one on projects. The part about when to retrieve and when to retrain comes from its guide to model accuracy, checked on November 12, 2026.
Common mistakes
- Uploading everything. Three price lists from three years give three different answers. Better a few documents, kept current.
- Expecting it to guess what isn't written down. If the terms for restaurants live only in the head of whoever runs sales, no path will find them.
- Naming nobody. Without a person who pulls what's expired, in six months it answers with old facts.
- Pasting sensitive data without looking. Before you upload anything, read what the tool does with what you give it.
When it isn't worth setting anything up
If the question is for today and won't come up again, stay on path 1. And if almost nothing at your company is written down, start by writing the essentials: without that, whatever you set up is an empty folder with a search box.