Can you be more specific in describing your situation? Hosts connect to an environment (also called tenant). Unless management zones (new beta feature, probably not yet enabled in your environment) are in place, you can see all hosts in the environment.
I am trying to understand by comparing Dynatrace ruxit with appmon. In appmon we can create system profile and point specific hosts& agents to that system profile,similarly in Dynatrace ruxit I understood that we can create environment(system profile),but how can we can we map certain hosts to that specific environment.
You can't create a separate environment yourself in SaaS, that is only possible for managed.
However you can use management zones to devide your tenant and split it up that way.