PartEditor  ConstraintsMenu and Toolbar
In the PartEditor, use the commands in the:
•  : to add sketchelements. This vertical and to the leftside of the graphicarea. 
•  : to add and edit constraints to and between sketchelements. This is vertical and to the rightside of the graphicarea. 
PartEditor: Constraints menu
PartEditor: Constraints Toolbar
In the PartEditor, the Constraints toolbar is to the RIGHTSIDE of the graphicarea.
MERGEPOINTS : Deletes a Point. You cannot remove a 'Merged Point'.
•  Use to join sketchelements endtoend, and remove one of the Points. 
COINCIDENT CONSTRAINT : Does not delete a Point. You can delete a CoincidentConstraint later and move the Points apart again.
•  Use to move two Points, or a Line and a Point, together. 
•  Use for 'construction' geometry. 

You cannot overconstrain a sketchelement in the PartEditor [SolidWorks will allow you, but give you a warning].
For example:
A Point has 2 degreesoffreedom [DOF]. It you add a 'coincident constraint' between a Point and a Line, you remove 1 DOF, and 1 DOF remains. The Point can slide along the Line.
You cannot add a further constraint between the same Point and a Point t the end of the Line, as a constraint between two Points try to remove two more DOF.

1.  Click a sketchelement in the: 
 or 
The sketchelement and the constraint show in the SelectionWindow.
2.  Rightclick the constraint in the SelectionWindow 
3.  Click 'Delete' in the contextualmenu 
