To get data via SNMP you need to know OID (Object IDentificator) or MIB (Management Information Base).
All available MIBs/OIDs possible to get via snmpwalk, as an example
#snmpwalk -v<version> -c <community> <host>
snmpwalk -v2c -c somecommunity 198.51.100.1
Frequently used OIDs:
CPU usage
percentage of user CPU time: .1.3.6.1.4.1.2021.11.9.0 percentages of system CPU time: .1.3.6.1.4.1.2021.11.10.0 percentages of idle CPU time: .1.3.6.1.4.1.2021.11.11.0 raw user cpu time: .1.3.6.1.4.1.2021.11.50.0 raw system cpu time: .1.3.6.1.4.1.2021.11.52.0 raw idle cpu time: .1.3.6.1.4.1.2021.11.53.0
Load Average
1 minute Load: .1.3.6.1.4.1.2021.10.1.3.1 5 minute Load: .1.3.6.1.4.1.2021.10.1.3.2 15 minute Load: .1.3.6.1.4.1.2021.10.1.3.3
Memory Statistics
Total RAM in machine: .1.3.6.1.4.1.2021.4.5.0 Total RAM used: .1.3.6.1.4.1.2021.4.6.0 Total RAM Free: .1.3.6.1.4.1.2021.4.11.0 Total Swap Size: .1.3.6.1.4.1.2021.4.3.0 Available Swap Space: .1.3.6.1.4.1.2021.4.4.0