Complex systems are made up of many interconnected parts that interact with each other in various ways. These systems can be found in nature, like in ecosystems, or in human-made environments, such as cities. The behavior of a complex system often cannot be predicted just by looking at its individual components, as the interactions can lead to unexpected outcomes. For example, the weather is a complex system where factors like temperature, humidity, and wind patterns all influence one another. Similarly, the internet is a complex system where millions of users and devices connect, creating a dynamic environment that evolves over time. Understanding these systems helps us tackle challenges in fields like biology, economics, and engineering.