Clicking in the Main Window allows you to select and move nodes and select elements. These features are only active when the Node Edit and Element Edit windows are active, that is visible on the screen and not iconified or dismissed.
When the Node Edit Dialog is visible, you can select the current node by clicking on a node in the Main Window.
If you click on a position other than a node, the current node will be moved to this location.
When the Element Edit Dialog is visible, the current element can be selected by clicking on the center point of an element in the Main Window.
Have only one of the Node Edit and Element Edit windows open at a time, so that mouse clicks meant for one window do not go to the wrong window. For example a mouse click not near enough to the center of an element, will cause the current node to move to that location, if the Node Edit window is active.