In normal C# programming without designer.cs (UI), shall we use partial class? How shall we use it in this case?

Question

I know the way to write a partial class in C# but i do not know when to use it.
e.g. If i am not developing using Windows Form or UI in C#, how shall i start design my class?

Java: Class
C#: Partial Class, Class

As above in C#, how shall we choose to use partial class and normal class ( assume no UI element in the application) .