A whole bunch of other excellent spline-modelling tutorials can be found at:

http://www.hash.com/users/jsherwood/

Greg M. Johnson wrote:

Here's a tutorial on splines, the basic beginner's version, not for
sPatch but for Animation Master.  The previously referenced tutorials
are good for experts, but I needed to see the content at the below link:

http://www.alienlogo.com/tincan/Spline-tut.htm