The server program fail2ban-server is responsible for monitoring log files and issuing ban/unban commands. It gets configured through a simple protocol by fail2ban-client, which can also read configuration files and issue corresponding configuration commands to the server.
For details on the configuration of fail2ban see the jail.conf(5) manual page. A jail (as specified in jail.conf) couples filters and actions definitions for any given list of files to get monitored.
For details on the command-line options of fail2ban-server see the fail2ban-server(1) manual page.
For details on the command-line options and commands for configuring the server via fail2ban-client see the fail2ban-client(1) manual page.
For testing regular expressions specified in a filter using the fail2ban-regex program may be of use and its manual page is fail2ban-regex(1).
Fail2Ban is able to reduce the rate of incorrect authentications attempts however it cannot eliminate the risk that weak authentication presents. Configure services to use only two factor or public/private authentication mechanisms if you really want to protect services.
A local user is able to inject messages into syslog and using a Fail2Ban jail that reads from syslog, they can effectively trigger a DoS attack against any IP. Know this risk and configure Fail2Ban/grant shell access accordingly.