Manually build spines
Manually building spines usually involves using the Path tool.
In the viewport, press Tab and type Path.
Draw the curve in the viewport.
Make sure the curve is selected, press Tab in the viewport, and type Bones from curve.
In the operation controls toolbar, set the Kinematics to Follow Curve.
If you move the handles, the bones will follow; however, they will not stretch with the spine. To make a stretchy spine you need to manipulate the length of all the bones with respect to the changing length of the curve. In order to do this you must use the arclen() hscript expression pointing to the curve.
Making bones stretch with the spine
On the Bone tab of one of the bones, use the arclen() expression in the Bone Length field. Each bone has to have a length equal to the curve diced up to the number of bones.
For example, in the following expression the division by fifteen represents one fifteenth of the length of the curve.
arclen("/obj/path1/output_curve", 0, 0, 1) / 15
Using the Auto Rigs shelf tools
You can also use the autorig biped and quadruped spine tools on the Auto Rigs tab of the shelf to create spines.
The 
Biped Spine and 
Quadruped Spine tools put down an Auto Rig Spine node and set the hook object parameter. However, these spines do not use inverse kinematics, and therefore do not have bones.
Note
If you ⇧ Shift + 
on the Biped Spine tool, you will get a list of different types of biped spines to choose from.
