There are a number of resources available to learn how to write programs with ispc.
To get started with the language, there is a walkthrough of a simple program written in ispc that highlights some of the main features and language constructs.
After reading the example, see the User's Guide, which provides a complete reference to the language and standard library. You may also find that the Performance Guide provides useful information about getting best results from the system.
The examples/ directory of the ispc distribution has approximately ten examples of using the language to accelerate various computations. All of these have reference serial C++ implementations, which makes it easy to compare the differences between ispc and C++ implementations of various algorithms. (You can also browse this code directly on github.)
A technical paper on ispc, ispc: A SPMD Compiler for High-Performance CPU Programming, by Matt Pharr and William R. Mark, has been accepted to the InPar 2012 conference. This paper describes a number of the design features and key characteristics of the ispc implementation.
Finally, there is a growing list of frequently asked questions (FAQs).