Smooth transition effect

hi there…

i was wondering how can i do the following effect…let say i have three buttons…buttonA, buttonB and buttonC. when i click on buttonA, the information lies in buttonA will appear on the stage…then when i click on buttonB, the information of buttonA will fade out first then only information lies in buttonB will appear. hope someone can give any idea or any link that teaches the effect step by step.

thanks in advance!