Customizing chatgpt

There is lot of data online around customizing chatgpt but not very clear.

I think at first you need to have your data in jsonl file in the form of (prompt, complation).
As far as I know, the preperation tool only add a special tokin to the end of prompt e.g., - > ,###**###, or add a whitespace character to the beginning of the completion. this help the model to identify the end of pormpt and the beggening of the complation.