There is a large amount of documentation in HIPE about HIPE itself, about the tools provided to visualise and work with data, and about the programing language used in HIPE. These documents are referred to as: URM: User's Reference Manual (the HCSS URM and the PACS URM), which is a dictionary of the tasks provided in HIPE; PDRG: the PACS Data Reduction Guides (PDRGs), spectroscopy or photometry; DRM: Developer's Reference Manual (the PACS DRM and the HCSS DRM), also known as java docs and which explains the capabilities and methods (i.e. how to use) all the classes in HIPE; the PDD (Herschel Product Definition Document), which is a reference guide for all the Herschel products.
A repository of PACS documentation can be found in the HELL archive PACS pages (it is best to open this in a new tab). A series of guides to PACS observations and PACS products, which are particularly recommended for those starting with PACS, can be found there. The Quick Start Guides for spectroscopy and photometry should be the first documents you read. A series of flowcharts guiding you through the various PACS spectroscopy products can be found in the Product Decision Tree. Finally, the PACS Handbook is recommended for those who wish to know more about the PACS instrument, its observing modes, calibration, products, and pipelines.