The Arduino IDE doesn't support breakpoints and other debugging methods, all you can do is to write on screen using gb.display.print, or send data through USB using Serial.println() (not supported by Simbuino).
I think that Simbuino allows debugging, but at low level (Myndale will tell you more).
If you want proper debugging on AVR microcontrollers, you'll have to use AVR Studio along with a JTAG (I never did so I can't tell more).
PS: don't worry about your English, most people are not native English here