MultiSite Help Please, What is difference between network site and first installed site?

I have never worked with MultiSite before and am trying to build a demo setup locally in preparation for a large scale network we hope to build. When I first installed WordPress I gave it a name of mastersite, and then I setup the network. Now I have two sites listed under “my sites” which are Network Admin and Mastersite. The Network Admin one has a ‘visit network’ link whereas the mastersite one has a ‘visit site’ link. Basically, what are the differences here? What is the main site? Did the site mastersite become the first ‘site’ of the network?

Also curious is I registered a new site from another browser and logged in, and that site shows both itself and mastersite under its ‘my sites’ tab….That confuses me! :slight_smile: So what IS mastersite now exactly?

Also, is there a way to have client/network sites ONLY see their site, no others in the ‘my site’ listing?

Thank you much.