Xdebug is a PHP extension which provides debugging and profiling capabilities. Most PHP IDE has built in integration with Xdebug, it works as below:

• set breakpoints at IDE
• click debug
• resume and continue to next breakpoint

As for the first glance, I still like Atom UI more. However phpstorm has some nice feature more such as code navigation, better debugging tool and less crash happen(however PHPStorm uses more memory).