Curves are objects that are expressed by mathematical functions rather than a series of points like meshes. There are a couple of types of curves that are available. Bezier Curves and Non-Uniform Rational B-Splines (NURBS). Both types of curves are defined in terms of a set of control points.
Curves can be added to the scene from the 'Add' menu found in the 3D viewport header.
The curve properties can be accessed through the curve properties menu (right-click mouse button when lamp is selected). Through the properties menu users can toggle between 'Edit Mode' and 'Object Mode'. Making modifications to a curve is done in 'Edit Mode'.
Curve 'Object Mode'
Curve 'Edit Mode'
While in 'Edit Mode' an additional menu is available that provides common tools needed to manipulate and modify the curve. This menu is called by using the 'Right-Click' mouse button (Edit Mode only).