Once you have a random key, you could have a database, an array, a list of files or whatever with a number (say 1-50) identifying each piece of tip text that you draw upon when the button is pressed.
The random number therefore determines which decision is made.
To create the button that displays the view is easy using UIKit, which I hope you are familiar with. If not, you should read up on views etc using Appe's documentation.
The tip could be displayed in a label in a modal view, or perhaps in a UIAlertView. The opportunities are endless... 😉