You can execute the code from anywhere, home is OK.
The machine always know where it is so depending on your Gcode, the machine will go where the offset(G54, G55...) is.
You need the machine to be at Zero (Home) and you need to set the Zero of the workpiece(WCS) or work coordinate system. This is G54, G55, G56 or G57..
If you hit the TAB key on your keyboard, you will see in which direction the arrows are pointing X+ will move to the right and X- will move the tool to the left.
This is always in relation with the tool.
So if the machine is at Home, when you hit start, the tool will go in the - direction, like X-20.000.
Can you post details of the breakout board your using.
In the home/motor and soft limits menu, be sure to check Auto Zero
Is your machine is similar the the one on the picture.
Jeff
Jeff