From an open Cmap:
Left-click on the concept you would like to make a new proposition from.
Left-click and drag from the arrows at the top of the concept. As you continue to hold the mouse button down, notice that an arrow from the selected concept will follow around the mouse pointer. (Another way to make the arrow follow the mouse pointer is to left-click once on the concept arrows, then release the button before moving the mouse.)
If you chose to drag the mouse from the concept's arrows, drag the arrow some distance away from the concept and release the mouse. (If you left-clicked once on the concept's arrows, let the arrow follow your mouse pointer away from the concept and left-click again.) A new concept will be created, along with a rectangle that connects the two concepts.
Type in a label for the rectangle, then left-click on a white portion of the Cmap to set the label. A linking phrase for the new proposition has now been created.
Left-click on the new concept and type in a label. Left-click outside the concept to set the label. A new and complete proposition has been created. A proposition can have more elements than two concepts and a linking phrase. You may apply the methods described in this help section as well as Create a Proposition from Existing Concepts to add to your existing propositions.