How to upload multi-files in GPT APIs and make a conversation?

I have a web app built with Laravel that connects to the GPT APIs to let users chat with GPT. Now, I want to add a feature where users can upload up to 5 files and have a conversation based on those files. I read the GPT documentation, and while it explains how to upload files, it doesn’t clearly explain how to use those files in a conversation. When I upload a file, I get a file ID in response, but I’m not sure how to use that ID in the chat.