If you are new the easiest way to set G54 is, in offsets set the X0 and Y0 using a edge finder if you have a block then that would be the left side and the front of the stock, Z would be set ( 0 )
Your Drawing in your cam program must match this X0 Y0 position also
Then in tool offsets set your tool to the top of the part, and the same in your cam software also the top of the part is 0.0 where the machining starts