It’s true: sometimes Macs do crash. More often than not, though, crashes will be limited to a single application, rather than the entire system.
You’ll know an app has crashed because it simply stops doing anything. Clicking on controls has no effect, scrolling gets you nowhere; the app simply doesn’t respond to your usual commands. So what do you do next?
First, don’t panic. OS X is designed to keep crashes under control. Even if an application has crashed, in most cases you’ll still be able to carry on just fine with work you’re doing in other applications. All you have to worry about is the one that’s crashed, and any unsaved work you had inside it.