Programming PLC controllers requires knowledge of various techniques and tools that facilitate the design and diagnostics of industrial applications. In this chapter, we will focus on several key aspects of working with controllers. We will start by analyzing errors that occur during program compilation and methods for eliminating them. Next, we will move on to creating a custom library, enabling the reuse of developed functions and function blocks across multiple projects. In the following section, we will discuss the CFC programming language by developing a sample program that controls a process variable. Finally, we will explore the Trace tool, which allows real-time monitoring and analysis of process variables – an invaluable feature for diagnostics and process optimization.