Linux monitoring my own ASUS router (MRTG)

[03Explorer]

I am learning what I can do with my equipment so I can bring to a customer site. I have a router in place and I want to fine tune MRTG to monitor my ports specifically. I have two routers bridged. I also want to monitor the 'other' second router to see if there is a performance drop between the two. I am running Linux and have SNMPWALK installed but uncertain how to effectively use. I am in a way dangerous enough with my knowledge but yet unskilled at the same time. Where is a good source to assist in identifying the ports. Get MRTG configured correctly and become a Ninja with SNMP all together.

I know this is a large ask, but I'm going to try here anyways!! )

Thanks in advance!