I have been hired as a junior programmer to work on projects that extend existing functionality in a very large, complex solution. The code base consists of C#, ASP.NET, jQuery, javascript, html and xml.

I have some knowledge of all these in addition to fair knowledge of object-oriented programming and its fundamental concepts of inheritance, abstraction, polymorphism and encapsulation. I can follow code up through its base classes, interfaces, abstract classes and understand a large part of the code that I read while doing this.

However, this solution is so humongous and so many things get tied together whenever I navigate through the code that I feel absolutely overwhelmed. I often find myself unable to fully follow everything that is going on with objects being serialized, large amounts of C# and javascript operating on the same pages and methods being called from template files that consist mainly of markup.

I love learning about code, but trying to deal with this really stresses me out.

Additionally, I do know that a significant amount of unit testing has been done but I know nothing about unit testing or how to utilize it.

Any advice anyone could offer me regarding dealing with a large code base while using Visual Studio 2008 would be greatly appreciated. Are there tools that I can use to help get a handle on what is going on? Perhaps there are things even in Visual Studio that I am not aware of. How can I follow the code to low level functionality in order to get a better grasp of what is going on at a high level?