How can I fine tune a gpt model

Assume I use OpenAI Platform by providing my own data (there is even an example on doing that in a subsequent paragraph of the same guide) : will this action trigger an update of 175B parameters? Where is the new model stored? Will this become a new model available for others to work on? (i.e. doing inferences) ? How correct is the belief that open source LLM models are cheaper to fine tune ?

I not sure in terms of how many parameters or if all of them are updated, but the changes made in the finetuning are quite visible.Honestly, never thought about it in that sense.

The model is only available to people in your organisation for usage , not to the rest of the world.