In Cacti, we do not need to work with Net-SNMP command line applications on a day-to-day basis. But we need to have knowledge on basic Net-SNMP command line tools to troubleshoot. If you are new to Net-SNMP, then a good place to start is the tutorial section: http://www.net-snmp.org/wiki/index.php/Tutorials.
According to the Net-SNMP manual, it is divided in different sections, such as SNMP basic applications, SNMP "second-level" applications, notifications, SNMP configuration, agent, SNMP base library APIs, agent APIs. We will not discuss details of each command; you can get the details in the manual page: http://www.net-snmp.org/docs/man/.