This article provides a detailed guide on how to send audio files to an Express.js server using Node.js and Multer middleware package. It covers setting up the backend server with Express.js, implementing Multer for handling different file types, creating a POST endpoint to receive data from the client-side, and sending audio files from the front-end using HTML forms or Javascript FormData objects. The article also explains how to configure storage options in Multer and handle multiple files uploads.