New Unity Programmer: Need Help with Buttons

I’m a new unity programmer for my Final Year Project, and I’ve only just been introduced to the Unity software and programming itself.

Right now, I’m trying to get my PSD buttons to work. I have 2 PSD files, one to show that is not clicked and one to show that it’s been clicked. I’ve no idea where to start so can anyone offer me any advice/help as to where I should start first?

The docs are always good: http://unity3d.com/support/documentation/Components/gui-Basics.html

go through the link
http://unity3d.com/support/documentation/Components/GUI%20Scripting%20Guide.html

it has everything in it related to GUI