This sets the movement limits for X and Y axes. If the software tries to move outside these limits, you’ll get a warning and the operation is cancelled. To set correctly, you need the visual homing to work. Home the machine with the bottom section “Home” button. The jog the machine to the end of X or Y axis so that the limit switch is quite not touched. Note the coordinate shown on the bottom section and put the number in the box.
The number is in mm’s.