Documentation for a given package can be found by following the link on that package's information page. Search the package list to find what you need.
The OCaml Package Manager (OPAM) is a source-based package manager for OCaml. It supports multiple simultaneous compiler installations, flexible package constraints, and a Git-friendly development workflow. For documentation on installing OPAM or packaging your libraries, read here. Packages are automatically tested upon submission and reports sent back to maintainers. If you submit a package, you will be rewarded with regular regression tests across many diverse operating systems and platforms.
OPAM has been created and is maintained by OCamlPro and OCaml Labs. Bug reports and feature requests for the tool should be reported on OPAM's issue-tracker. Packaging issues or requests for a new package can be reported on the main repository's issue-tracker. General queries for both the tool and the packages can be addressed on the OCaml-platform mailing-list and insights and evolution of OPAM internals can discussed on the OPAM-devel mailing-list.
There are a number of excellent books, with two new titles published in 2013. Real World OCaml is available to read online.
In this talk, Mark Shinwell explains how to track down hard-to-find bugs in OCaml programs. It involves the new gdb functionality which OCamlPro and others have worked on recently. ( PDF slides)
Talk at CMU describing the experiences that Jane Street has had using OCaml as it's primary development language.
Experience Report: OCaml for an Industrial-strength Static Analysis Framework Pascal Cuoq and Julien Signoles; CEA LIST International Conference on Functional Programming (ICFP) Edinburgh 2009.