These vector tools are used to create simple geometric vector layers.
By holding Shift you create a layer with equal height and width.
If the active layer is a vector layer and you are holding Alt while dragging, no new layer will be created, but the vector object will be added to the active layer. If the active layer is an image, the vector object will be drawn in that image. If Edit Mask (see chapter 4.5.2.4) is turned on, the foreground color (see chapter 4.5.2.1) is used for drawing in the mask. If the Ctrl-key (Windows) or Command-key (Mac OS) is pressed, the background color will be used.
Use the tool options dialog to setup shape specific options like corner radius, corner count of stars, ...
The Ruler tool can be used to create editable rulers. The tool options allow to control, how many units are shown in the entered area.
The tool options can be used to edit existing layers, too, if they were created with one of those tools previously.