identifying OTU interactions / hubs
I am going to assume you have a count table that you are starting with. Every tool you decide to use is going to have its own respective instructions so let me get you pointed in a direction to find one that works for you. 

I wrote a simple R package for my lab awhile back but there are much better ways to put together Co-occurrence networks (in no particular order):


SparCC
CoNet
MENA
Spiec-Easi
MDiNE 


Now speaking specifically about "hubs", "connectors", and other keystone organisms, I would recommend reading more about what they are and how they were developed. Again, I have a brief summary here but the original "hub" came from a paper on bee pollination networks