Whilst the manual states that the triangle will be visible if you connect the vertices to "form a clockwise pattern relative to the viewer", this makes no sense to me; For starters, the "viewer" doesn't -exist- in 3D space in any form other than the camera; And the camera position and direction does not appear to effect the direction the triangle faces.
Defining the position of verts and the order they are joined to form triangles is purely conceptual and relative to the local origin of their object, the camera has nothing to do with that process whatsoever. However, when you eventually *do* have a camera, which triangles get rendered will depend on the direction they face relative to that camera, and the direction they face will be dependant on the position and orientation of the object in question.
So, the manual's comments are there to explain the rendering rules you must keep in mind when describing your objects. For example, the triangles on the opposing sides of a cube must be described in opposite directions for them both to face outwards (the "front" ones clockwise, the "rear" ones counterclockwise).