NURBS or Non-Uniform Rational B Splines uses splines (curves) as the foundation for all surfaces built.

Polygonal model is based on geometry where surfaces are made of 3, 4, or n-sided faces.

Subdiv is sort combines the two, allowing to built in polygonal fassion while retining NURBS like smoothness.

Vastly oversimplyfied explanation...

To warm up, use the training video with PLE, go through tutorials in the help files, try some of the free tutorials on this site and others like it.

post your work in the forum and as for feedback. Congrats on your first steps into 3D, you'll never look at the world the same again.