The basic idea of a partial class is very easy to understand. You keep the definition of a class split into pieces. During the compilation of the code, the compiler will finds all of the pieces of the class and lump them together. This task accomplished by the compiler removes that separation, so functionally there is no difference between a class made of partial classes and a whole class.

This is great because it means that we get the benefits of being able to develop applications using partial classes without fear of it having any affect on the functionality of the code we write.