The Toolbox is a habitual approach to typical CG tools.
Ruler: 
When you select the Ruler, your current brush does not change. It can be a pencil, marker, or oil brush – all it will draw straight lines until the Ruler enabled.
Use “Center point”(1) To move Ruler.
Use “Angle point”(2) to rotate Ruler.
Use “Cancel button”(3) to disable Ruler.
You can draw not only on Ruler edge but on any place of the canvas – all lines will be parallel (4)
Cutters:
Craft cutter
Craft knife
These tools are the interpretation of the typical CG soft “Lasso” and “Rectangular selection” tools. Cutters replace the last selected brush as an active tool.
USAGE:
1)Select the required area and then choose any brush to draw inside the selected area (2). Also, you can use Сalipers (Free transform) to modify the only selected area.
Click the Cancel button(3) to remove the selection.
Default hotkey: Ctrl+H to hide selection
Scissors
Scissors work like a lasso selection but immediately erase selected area.
Drawing compass
Drawing compass allows to draw circles. It works the same way as the Ruler tool.
Сalipers
Calipers are a “free transform” tool. Use it to resize the layer or selected area.
To confirm click 
button or press Enter.
Also, you can change the perspective of the layer. To do it hold CTRL key and drag the corner of transform.