Your tools can all be entered in the tool table - see Config/ToolTable.
Tool 0 is not shown but it the base setting of the table, with all offsets at 0.
You really need a quick change tool holder or similar fixture on your machine to use the tool table, since all offsets are measured from this, and the position of each tool can be guaranteed when you put it in.
My 0,0 position is taken from my empty tool holder. It doesn't matter where, but it should be some position that is readily recognisable and you can measure from it.
If you take my lathe (although the same applies to a mill if you follow it through) my home switches set the machine at 0,0.
My g55 offset (say) then sets the machine at a position where x0,z0 is level with the chuck jaws, and on the centre line of the lathe with an empty tool holder in the fixture.
My tools are entered in the table with their offset in relation to this i.e. they protrude "*" inches from the tool holder, and are "$" from the front. Therefore when I select a tool T0101 for example, and then ask the machine to go to x0,y0, the machine moves so the tool tip is at x0,y0. Repeat this for all the tools you are going to use.
I even have centre drills set in a holder at the rear of the cross slide, and if you call up the relevant tool number, then the machine will move the cross slide into line with the drill holder in the centre of the lathe, an appropriate distance from the workpiece to begin drilling.
The same applies to a mill, but the GCode is M6 T (whatever)