Auxiliary lines are very helpful to position symbols exactly. Auxiliary lines are displayed in the specified distance (mm), beginning from the bottom of the drawing area. The separator for the values is the '#' character, the decimal separator is the '.' character. You can enter up to 10 values to get up to 10 lines.
Auxiliary lines can be created by short cuts directly in the schematic. Press Ctrl+(-) for horizontal lines and Ctrl+(|) for vertical lines. If you do the same at the same place you can delete the Auxiliary lines.