Hassan-
Breakpoints are a way for you to trigger another device, based on the location or velocity of your motor. Please refer to the NI-Motion users manual (link provided below), specifically Chap 12, for a complete description about breakpoints and how to use them. Thanks.
http://digital.ni.com/manuals.nsf/websearch/D4234B354DFA64568625717F00735842
John H
Applications Engineer
National Instruments
http://www.ni.com/support