Network Enumeration

I am newbie to this list and curious to know a couple things on how to
proceed with doing network enumeration. I was looking for some assistance
on how to utilize NMAP or any other tool, and I will be using Nessus to
import the findings to do a scan on that file (using the NASL).

If there are any online or other resources that will help with getting
information on this topic??

Thank you,

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