Hey Tony,
in front of coordinates, you need a motion command like G0 (rapid move):
G0 X0 Y0
This will go to the X and Y zero coordinate of the currently active coordinate system. If you’ve probed or set a workpiece zero manually with G92 (set coordinate system offset), then it will go there. If no offset coordinate system is in effect, it will go to machine zero X and Y (=home position of X and Y).
If no offset coordinate system is in effect, then the command
G0 X405 Y316
will move to this position relative to machine zero.
Then, if you want to make this position your new workpiece zero, you enter G92 (set coordinate system offset). From then on, every subsequently entered coordinate will be relative to your new workpiece zero which is here.
There is only one way to reach this: Try it out as often as possible and see what the machine does. G-code doesn’t bite, it just wants to play 
Here is the G-code reference:
- Complete LinuxCNC G-code Reference (Buildbotics G-code was modeled after this)
- NIST RS274NGC Standard
- G-code – Wikipedia
- Cheat sheet of all G-code commands available on the buildbotics-derived Onefinity CNC Controller (also available on the User Interface of your Onefinity controller under “Cheat sheet”)