You can set breakpoints when you want to stop debugger execution, perhaps to see the state of code variables or to look at the call stack. They are one of the most important debugging techniques in a developer's toolbox.
You can set a line breakpoint in source code by clicking in the left margin of a source code file, or by putting your cursor on a line of code and pressing F9. The breakpoint appears as a red dot in the left margin, and the line of code is coloured as well:
When you run this code in the debugger, execution stops whenever the breakpoint is hit, before the code on that line is executed. The line of source code is coloured yellow:
At this point the value of testInt is still 1.