Watch this video to understand the need for debugging.
Starting the Debugger
To debug an ABAP program, you set a breakpoint then run the program normally. When the program reaches the breakpoint, the system interrupts it and opens the ABAP Debug perspective in ADT. You can then execute each subsequent statement individually to see what effect it has on the program. You can also inspect the contents of all of the variables in the program to see if any of the values are unexpected.
To set or remove a breakpoint, right-click the left margin of the editor and choose Toggle Breakpoint. As an alternative you can double-click the left margin. Note that the program has to be activated before you can set breakpoints.
Breakpoints are user-specific and are persistent - they remain active even after you have logged off from ADT and back on again. To prevent the debugger from starting at a breakpoint you must either delete the breakpoint (using the Toggle Breakpoint function) or deactivate it using the corresponding function in the context menu.
The Debug Perspective in ADT
When you debug an ABAP program using ABAP Development Tools, you use the Debug perspective. This is a customized version of the standard Eclipse Debug perspective, and it contains views and functions that are particularly important for debugging.