Please check out https://f5.com/education/training and see if the "Getting Started: APM" will help for you. You'll need a support login.
Also check out: https://devcentral.f5.com/wiki/APM.HomePage.ashx
https://devcentral.f5.com/articles/irules-101-01-introduction-to-irules
The 101 iRule articles/wiki will get you up to speed on iRule functionality; combine that with the APM tutorials and you should have enough to get you started on the iApp functionality and modification. Beyond that, more advanced training is available through university.f5.com.