How do I know what version I'm using?

You can identify what version of the software you are using from the About window, also called the About Box.

On Windows

If you're using any Windows version, you can access this window from the Help menu by choosing the "About..." menu option.  In the case of My Checkbook, it would be called "About My Checkbook..."

On Mac OS X

If you're using any Mac OS X (also called OS X), you can access this window from the "application menu" which has the same name as whatever application you're using.  So, for the case of My Checkbook, the menu would be called "My Checkbook"