xdebug is an immensely powerful tool for exploring what your code really does.

You can get a long way using print_r  but ultimately this always requires that you predict the path your code will take - and the tricky bit about debugging is you need it when your predications have gone wrong.

It's generally pretty easy to set up

• install the php5-xdebug package
• check that the Eclipse PHP preferences have xdebug as an option
• if you're debugging locally the default settings should be OK
• create a site configuration in the debug dialog
• set a break point
• start debugging

If it doesn't work at first restart Eclipse

Check that you have a browser configured in Eclipse

Not all settings seem to be picked up immediately