Programming a texture to act as a button...

Hello,

I just recently moved from Flash over to Unity and I am having a hard time understanding how things work. I finally got my texture atlas working and have all my textures loaded onto the start screen of my application. I want to program my start texture to be a button so that when I click on it brings me over to another scene where you select the game level at. Any help with this would be greatly appreciated. Keep in mind that I am a beginner and don't know much about unity.

Thanks