Each report type will have different data included. Definitions of the terms used in the reports are available in the Calculations Guide along with info on how the numbers in each report are calculated.
Here is an example annotated Target Segment Measures report showing how likely someone is to vote in a Presidential election based on the amount of education they've received.
Nielsen SMS's Frequently Asked Questions document has some tips and best practices for using Nielsen SMS. Here are a few:
How many segments should I pick for a campaign?
What is an index? How do I interpret?