Dear Francis,
Please see the Linear Fresnel Overview topic in Help for a description of the model components. Unfortunately, the overview does not include a diagram, but hopefully the description is clear enough:
Linear Fresnel Overview
You can also access the Help system from SAM by pressing the F1 key in Windows, or Command-? in OS X.
I answered your question about weather files for non-U.S. locations where you asked it in this thread:
Specific Site and DNI
Best regards,
Paul.