All of the editing operations are performed using the left mouse button. This is equivalent to the single mouse button if using a one button mouse. When a right mouse button is available, this can optionally be set as a shortcut button to delete a stitch.
Initially the Right Mouse Button stitch delete feature is not enabled but can be either enabled or disabled through user preference. See Preferences for details of how to open the Preferences dialog. Set preference setting Enable stitch delete with right mouse click as desired.
Once the Right Mouse Button stitch delete feature is enabled and either the Arrow Selection Tool or the Drawing or Painting Tools are active, then a right mouse click will cause the stitch directly under the cursor to be 'deleted'. A stitch is not actually 'deleted' but is reset to the default stitch which is a knit stitch in the default yarn.
This is equivalent to selecting a stitch and then 'deleting' the stitch using the Delete icon from the toolbar or the delete or backspace keys.
Alternative sources of explanation: