Getting communication with devices
Once you have a device to talk to with, say, IP 192.168.0.100, use the snmpwalk command to communicate with it, as follows::
$ snmpwalk -OsS -c public -v 1 192.168.0.100 private
This will query the device for all variables under the "private" node.
What is SNMP (Part 1 of SNMP Tutorial)
To get a value of a specific variable, replace the "private" word for the name (or the SNMP path/code) of the variable. If you are using the name, don't forget to properly install the MIB database so net-snmp can recognize variable names. For installing a MIB database, see net-snmp FAQ:
Net-SNMP FAQ: How do I add a MIB?