All Joomla versions use PHP and when it encounters a php problem it displays them in the form of warnings, notices and errors - this enables you to troubleshoot php problems.

Warnings are the least important, followed by notices and then errors - errors are by far the most serious as these mean the script has not executed and can cause a white screen to be displayed.

To find out more about error reporting and see a practical example -

docs.joomlabamboo.com/joomla-basics/how-to-enable-error-reporting-in-joomla-25
www.joomlabamboo.com/blog/how-to-joomla/how-to-fix-a-blank-screen-after-upgrading-to-joomla-3-2