Breakpoints are temporary markers you place in your program to tell the debugger to stop your program whenever execution reaches that point. For example, if a particular statement in your program is causing problems, you could add a breakpoint on the line containing the statement, then run your program. Execution stops at the breakpoint before the statement is executed. You can then check the contents of variables and the call stack, and step over (execute) the statement to see how the problem arises.
To add a breakpoint: