debugging php webapps

Hi. Looking over different articles.. Figured I'd post here as well. What tools are used to debug webapps/php apps? Treat the user/reader as a 6 year old! What setups, what tools, what sites have you found that detail the "tricks" I'm looking at firing up some bootstrap/laravel webapps, and I'm going to want to get to the level of understanding "as fast as possible" regarding front-side/serverside interaction, and/or bootstrap integration to laravel. thanks much!