A basic knowledge of object oriented programming is assumed. There are many books on the subject. A popular book is Object Oriented Analysis and Design with Applications by Grady Booch. There's also The C++ Programming Language by Bjarne Stroustrup.
In addition to reading about the basics of object oriented programming, I strongly recommend Design Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides.