Here is a 1-paragraph summary of the text: The OpenAI API provides access to GPT-3.5, a machine learning model that can chat, answer questions, and help with language tasks, but it has limitations due to its training data only going up until 2021. To overcome this, lLamaIndex is used as an open-source framework to connect internal data sources with GPT-3.5, enabling tailored responses based on proprietary data. The tutorial guides users through setting up a project for their chatbot, building and improving it using lLamaIndex, and evaluating its performance using DeepEval, which provides a platform for evaluating and testing LLM applications, fully integrated with DeepEval.