As for how we know which Contacts belong to which Accounts we have a few ways of doing it:
Once that's working, following Accounts works just like following Contacts.
Accounts in Variance have Properties. This is where you can store information about the Account. You can update these via Segment or Rudderstack and from your CRM via Zapier. You'll also notice the domains associated with the Account under the name.
We know that it's hard to always have data stay clean, sometimes two of the same account or contact show up. You can merge those together in a non-destructive way that will simply tell Variance that all of these Accounts and Contacts are the same.