3-D lines, or chords, are represented as  zero-based, one-dimensional arrays that contain two elements:  the starting 3-D point and the ending 3-D point.  A 3-D line can be constructed in a number of different ways.  For example,

Dim arrStartPoint, arrEndPoint, arrLine

arrStartPoint = Array(1.0, 2.0, 3.0)

arrEndPoint = Array(4.0, 5.0, 6.0)

arrLine = Array(arrStartPoint, arrEndPoint)

RhinoScript contains a number of methods to manipulate lines.  See Lines and Planes for details.