I want to make a powerpoint slideshow where in one slide I have the equation: If x = 3 then what is y in x + y = 5. When user taps any key, y=2 appears. How do you do this? I've never seen it described online.
This is called animation. First, you create the different elements, maybe using different text boxes. Then define animation for each element. Depending on your PowerPoint version, the exact steps will differ. In PowerPoint 2003, choose Slide Show> Custom Animation. In 2007, go to Animations tab> Animations group> Custom Animation. In 2010, go to Animations tab. The Custom Animation task pane appears in 2003 and 2007, but not 2010.
For a more detailed tutorial see Ellen Finkelstein's Tutorial on animation and best practices