If you are using Mach3 click on the "G-Codes" button on the Program Run screen. Scroll down to G10 for an explanation of it's purpose. I'm no gcode expert but after reading it through quickly G10 is used to define your tool and work offsets. My only experience is with G54 which I set to 0,0,0.
Zero offset or work shift.
It will shift your 0,0,0 to another position and run the program there, this is useful when making multiple parts on one fixture or in several vices. Do not forget to turn it off with G11 or the offset zeros remain in effect until program end.
For example if drilling a bolt circle in three identical parts in one vice it would be far simpler to shift the X axis zero to the right then to program all from the original point. This becomes slightly more complicated when automatic tool changes are involved.