This chapter covers classes and objects, the most important building blocks of OOP. These are the two things that we should learn before jumping into any other topics in OOP. It is important to make sure that these concepts are clear in our minds before moving on to other ideas. In this chapter, we learned about what a class is and why it's needed in OOP. We also looked at how to create a class in C# and how to define an object. After that, we looked at the relationship between classes and objects and how to instantiate a class and use it. We also talked about variables and methods in a class. Lastly, we covered the four pillars of OOP. In the next chapter, we will learn more about inheritance and class hierarchy.