How to use the standard reports RKPDEMO2 in a customized program

Good Day, I am creating a cusromized program to get all budget amounts in gross value. I tried to debug the t-code S_ALR_87013558 to find how it came up with the value. I am looking for tables or function modules that could help with the project. I came across a report RKPDEMO2. Unfotunately i dont know it works and its flow, can any one help me to understand this report? Thanks in advance.