If you are programming in Cent 5 conversational , one of your first lines should be misc/work coord . use the f3 key to toggle to work 1.
then you should be using the jog/handwheel to locate and set your x/y zeroes .
In G code , work 1 is G54
every time you fire up the machine , you have to home it , as long as you call up g54 , you will go back to the same zero pionts .
BTW you also have 5 more work coord if you jig up multiple parts