When the various point snaps are switched on, a coloured indicator is displayed when the mouse cursor is close to a key-point on an existing element allowing a perimeter or partition line end-point to be positioned precisely at the selected key-point.
See also the Blocks and dimensioning protocols and Adding blocks and using the measure tool tutorials.
The following point snaps are available:
Note: In some cases Snaps can interfere with attempts to draw to a particular point and in this case you can temporarily switch off the appropriate snap(s) using the check boxes in the Drawing options panel in the bottom left of the screen.