The XTTS (eXtended Text-to-Speech) model is a high-quality open-source text-to-speech system that offers multilingual speech synthesis capabilities. To run XTTS using Modal, a serverless cloud computing platform, users need to create an account at modal.com, install the Modal Python package, and authenticate their account. The script uses a single Python file to set up and run XTTS, importing necessary libraries and setting up the Modal app, defining the image that will be used to run the model, and implementing the XTTS class with methods for loading the model and speaking text. The script also defines an entrypoint function to run the XTTS model, taking a text input and saving the output as a WAV file. To use this script, users need to save it into a file, run it using Modal, and provide the text to be converted to speech.