To add nodes to the cell:
Nodes are always placed at the intersection of three grid lines. As you move the mouse over the cell, a line of potential nodes along a grid line is displayed. That line always starts at a back or bottom wall of the cell, as seen from the current perspective. Thus, it is always one of the three walls whose grid is displayed in the screen. The displayed line of nodes starts at the closest intersection of grid lines to the mouse cursor. It represents all possible nodes along the grid line leading into the cell from that intersection.
Nodes may also be added by specifying exact coordinate locations on the Node tab.