What is it?
MathSciNet is a database that provides reviews of books, book chapters, and journal articles in the field of mathematics, statistics, and related fields.
This user guide covers the basics:
To maximize your search click Show All Fields, which is to the right, and just underneath, the basic search box.
Then see the Standard tab and Advanced tab for help with searching particular fields--like Title or Author
See the Syntax tab for help with:
How to search with multiple words
How to search with the Boolean operators AND/OR/NOT
How to do a wild card (*) search

More help can be found here.