How to understand about structural equation modeling

Let's go to analyze
SEM analysis consist of two technics:
1. Covariance based
using AMOS or Lisrel -based on normality assumption
when we need amos? answer: estimation
2. Variance based
using SmartPLS, PLSGraph, etc - based on nonparametrics measurement
when we need PLS? answer: prediction
take looks these links:
http://zencaroline.blogspot.com/
http://zencaroline.blogspot.com/2007/06/useful-sem-website.html