The <ipp_directory>/Documentation/en_US/ipp directory, set up during installation, includes a lot of helpful documentation related to Intel® IPP. See the ipp_documentation.htm file for a listing of all the available documents with links or pointers to their locations.
Additional documentation on the high-level APIs is available with the IPP samples:
UMC: <ipp samples directory>/documentation/umc_manual.html
UIC: <ipp samples directory>/documentation/uic_manual.html
USC: <ipp samples directory>/documentation/usc_manual.html
The IPP forum and knowledge base can be useful locations to search for questions not answered by the documents above. Please see: http://software.intel.com/en-us/forums/intel-integrated-performance-primitives/ .