Having established the fundamental concepts and mechanics of Large Language Models, the focus now shifts to practical application. This chapter guides you through the process of interacting with models that have already been trained on extensive datasets.

You will begin by understanding what constitutes a "pre-trained" model and why using one is often the most direct way to start applying LLM capabilities. We will then cover methods for finding and selecting suitable LLM services or platforms. The practical sections demonstrate interaction through common web interfaces and provide a basic introduction to using Application Programming Interfaces (APIs) for programmatic access. This includes structuring simple API requests and interpreting the responses generated by the model. The chapter concludes with a hands-on exercise centered around a basic text generation task.