From an open Cmap:
Starting with two or more concepts, left-click on a 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, select another concept to drag the arrow over and release the mouse. (If you left-clicked once on the concept's arrows, let the arrow follow your mouse pointer over another concept you have selected, then left-click again.) A rectangle will appear with lines connecting to both concepts.
Type in a label for the rectangle, then left-click on a white portion of the Cmap to set the label. The rectangle will dissappear, leaving a linking phrase in it's place. The linking phrase completes the proposition. 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 New Proposition from One Concept to add to your existing propositions.