The manual page for
ssh_config is the penultimate authoritative source on that. Only the source code is higher. We could only paraphrase either here so scroll down in the manual page for the client configuration file to find the explanations of those options:
There are also pages for the client itself, or the server and its configuration.
Code:
man ssh
man sshd
man sshd_config
You can also search forwards in the manual page with a slash and backwards with a question mark. The OpenSSH manual pages are particularly well-written.