The frequently-asked questions (FAQ) is available.
Information about the first-ever open source FIPS-140 validation is also available.
The manual pages for all supported releases are available. There are still problems with some of the links; thanks for your understanding.
Ivan Ristić, the creator of https://ssllabs.com, has a free download of his OpenSSL Cookbook that covers the most frequently used OpenSSL features and commands. It is updated often, and is available at https://www.feistyduck.com/books/openssl-cookbook/. It is highly recommended.