First questions about Bussiness rules!!!

Hello to every.

In a message before this one, I said that I'm junior in SAP. I've just started to work in a SAP proyect and I have to make for mi boss, one first manual about How to use BPC. My situation is below:

I copied the default application set into a new one. Then I created an application with some new dimensions. And now, it starts my problem. I have manuals about bussiness rules but I cant undestand almost anything.

In the application, I have a folder called: bussinees rules with any of them. There I can introduce new registers in them (although I dont know how to use them =( ... ). After that I see another folder called script logic with default.lgf and legalconsolidation.lff.

In a manual I see that to call bussiness rules , in this files.lgf you can invocate them with sentences.

¿¿Mi first question is: when I have to call this .lgf??? ¿¿¿is automaticlly invocated when datas are sent to the server and when I execute "Data Manager package " such as I see in the manual?????

My second question is "what is Data Manager package "??

All of this, more or less can be understood but then I see That I can use MDX or SQL to script logic???? for what??? script logic are not the fields which call files.lgf????

My last question is for what is used Business rule library???

I'm in a trouble!!! =(

Anybody can make me a resume???? =( pleaseeeeeeeeeeeeeee!!!