When the workbench is running an application and encounters a breakpoint, the application temporarily stops running. Execution suspends at the breakpoint before the line is executed, at which point you can check the contents of variables and verify the information on the stack frame. You can then step over (execute) and see what effect the statement has on the argument or you can choose to skip execution of the statement in question.
With the debugger, setting breakpoints is easily accomplished with click actions or pop-up menus in the editor. Once set, you can disable breakpoints so that they do not suspend execution and then, later, enable them again.