I’ve seen it happen many times now…

People assume Apple’s Mighty Mouse only has one button.
It’s actually got quite a few, you simply have to enable the right side to be the ’secondary button’, and that’s done in Keyboard & Mouse under System Preferences.
Here’s how you enable it:
- Click the Apple in the upper left corner of your screen.
- Click System Preferences.
- Click Keyboard & Mouse.
- Click the Mouse tab.
- On the right of the Mighty Mouse, click the box, and…
- Select “Secondary Button“.
Here’s what it should look like when you’re done:

Also, while you’re in the Keyboard & Mouse preferences, you might want to change the Keyboard Shortcuts so you can tab through dialog boxes on your Mac, and on the web.