LangChain is an open-source tool used to interact with large language models (LLMs) and build applications around them. AssemblyAI offers transcription models for transcribing audio files into text, which can be used in LangChain. This tutorial demonstrates how to use AI to answer questions from a Twilio Programmable Voice Recording using LangChain.js, AssemblyAI, and Twilio Assets with Node.js and TypeScript. The process involves setting up a Node.js project, recording an inbound phone call to a Twilio number, transcribing the call, uploading the transcript to Twilio Assets, and creating a JavaScript application with LangChain.js to answer questions about the Call Recording file.