ABAP programs should start with statement PROGRAM or REPORT. Thsi statement will tell SAP in runtime that you are running a report program or modulepool program.
The PROGRAM statement is used for general ABAP programs (for example, module pool programs).
Start any program with all the data declaration and constant declaration required.
After that the main processing block starts. Here modularisation, perform needs to be done, which will be covered in coming posts.
All the name of the constants, variables, internal table etc should be as per clients naming standard. Every client has there own naming standards.