about what? You asked how to view the source code... I figure you meant the source of a custom class, profile or plugin... since they are text, opening them up with a text editor is the answer.
As for what you are looking to edit, we are not psychics - we have zero idea of what specifically you are referring to. You asked a general question, I gave a general answer.
You want a specific answer, then ask a specific question. What are you referring to, what is it doing or not doing that you want it to, what do you want to change?? I may or may not be able to help you, but if you ask a specific answer, others might.