Tutorial on how to create an AI Agnet

Hi, I need a step by step tutorial on how to create an AI Agent. Basically instant to teach a GPT with the workflows of our company, so all SOPs, user data, telephonennumbers etc. I am working with ChatGPT so if a project within ChatGPT would be possible that would be great. My aim is that employees can ask a chatbot via WhatsApp on how things are working, e.g. „who do I have to call to get information regarding my payment“-> Chatbots sends the number of our tax people. How can I perform an ecg-> chatbot explains step by step with the information we initially provided. The knowledge should be expandable.
I also have a zapier account and don‘t know much about it….
So my aim is to build it by myself that is why i need a step by step guide.