To view or change details of a variable or other object in a diagram, you must first select a node (or a set of nodes). You do this in much the same way as you select files or folders in the Windows File Browser, and most other applications:
To select a node: Simply click a node once to select it. Selected node(s) are highlighted with reverse color in browse mode, or with handles (little corner squares) in edit mode. You can also press the Tab key to select a node. Each time you press Tab, it selects the next node in the diagram, in the order the nodes were created. Control+Tab cycles through the nodes in the reverse sequence.
To select multiple nodes: Click a node while pressing the Shift key to add it to the set of selected nodes. You can remove a node from the selection by clicking it again while pressing Shift. In edit mode, you can also select a group of nodes by dragging the selection rectangle to enclose them. Press the mouse button in a corner of the diagram — say top-left — and drag the cursor to the opposite corner — say bottom right. This shows the selection rectangle and selects all nodes within the rectangle.
To deselect all nodes: Just click the background of the diagram outside any node.