iDempiere is a complex ERP with an equally high learning curve. Unfortunately, finding the correct iDempiere documentation takes time. You have to be patient and adept in finding the resources and documentation you need. Thus, Google will always be your friend in learning iDempiere.
To help you to learn about the system, you can start with the main idempiere website i.e. www.idempiere.org. The site contains the basic information you need to learn about iDempiere. You can also ask questions in the main idempiere forum if needed. You can check http://wiki.idempiere.org/en/Communication_Guidelines for iDempiere’s communication gudelines.
As iDempiere is a fork of aDempiere, Compiere and is similar to Open Bravo, documentation from these other systems may help. There were two books for aDempiere which were written many years ago, namely, Adempiere 4.0 ERP Solutions and Adempiere 3.6 Cookbook. These are also good references to learn iDempiere. However, you will need to filter the information and determine which would be applicable to iDempiere. The core of these applications are similar but there will definitely be differences as each application took a separate path after each fork.
You should also note there is no central repository of iDempiere documentation. You will need to be skillful, patient and resourceful to find the documentation and learn iDempiere. Learning iDempiere takes a lot of patience, passion and commitment. However, once you learn the application, you will unlock and appreciate the power of iDempiere and how it can support a Philippine business.