1.2 Required skills

PHP OOP

First, you need some programming skills :). We recommend the courses from teamtreehouse.com:
https://teamtreehouse.com/tracks/php-development

These courses are not free, but teamtreehouse.com offers a 14-day trial.

Symfony basics

To start out. you need to learn Symfony. You can find good tutorials at:
https://knpuniversity.com/

KNP university is a paid service. Free tutorials are available all over the web. We recommend searching for them because they change often.

After that it is also recommended to read the Symfony Cookbook:
http://symfony.com/doc/current/cookbook/index.html

MongoDB ODM

As Integrated uses MongoDB heavily we recommend having some knowledge about it. 

We recommend the Doctrine MongoDB ODM documentation:
http://doctrine-mongodb-odm.readthedocs.org/en/latest/

Working with Composer

Integrated uses Composer for package management. You need to know some composer basics. We recommend this courses from teamtreehouse.com:
http://teamtreehouse.com/library/php-standards-and-best-practices

These courses are not free, but teamtreehouse.com offers a 14-day trial.