At the network level the Pointer tool is used specifically to manipulate the current selection, move the current selection around, reconnect links and for re-scaling. At the dialog level it is used to select a data item or to position the cursor for editing text.
The "current selection" is the set of objects which many menu commands operate upon. Objects that are members of a selection are indicated in inverse video (bright magenta). To make a single object the current selection, just point to it and click.
To select a group of objects in a single operation the mouse button is held down and the dotted outline of a box is dragged around the desired group. To deselect everything, the mouse is clicked in open space. All the objects in a path between two nodes can be selected by first clicking on one node, then, with the <Ctrl> key held down, clicking on the other end node.
To extend a selection, the <Shift> key is held down in conjunction with the selection operation. The <Shift> key causes new selections to be toggled. The only exception is Background Picture Objects which must be modified while holding down the <Ctrl> key.