The frequently-asked questions (FAQ) page is available.
A good starting point for understanding some of the key concepts in OpenSSL 3.0 is the libcrypto manual page. Information and notes about migrating existing applications to OpenSSL 3.0 are available in the OpenSSL 3.0 Migration Guide
The manual pages for all supported releases are available.
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.
Historic information about our legacy OpenSSL FIPS Object Module (FOM) 2.0 FIPS 140-2 validation is also available.