To build a WhatsApp chatbot, developers can use Twilio, Dialogflow, and PHP. Natural Language Processing (NLP) enables computers to understand human language, allowing for more nuanced interactions. Dialogflow provides a natural language understanding engine that allows users to build conversational interfaces. To set up the project, developers need to create a new directory, install required dependencies, and activate their Twilio sandbox and Dialogflow account. The PHP fulfillment webhook receives user input, processes it, and provides an appropriate response. Developers can test the webhook by sending messages on WhatsApp and observing the responses from the chatbot. With this setup, users can build simple chatbots for various applications, such as restaurant booking or online store support.