You are logged into your system. In this case, it's macOS. You are facing just a simple question. Are you the only one who is logged in? I would like to give you an answer to this simple question with a bit of explanation. Here in upcoming lines, there will be a bit of theory background behind it.
In case your system is healthy (understand as an official system with applied updates), you are the only physical user logged in. You can check this logged in information with a simple command you will enter into the terminal. But there is a trick in that, will explain in next lines hereunder. Open your
Terminal.app you'll find out in
Finder in the section
Utilities. For more informations check official Terminal User Guide.
uptime command you'll be informed in one line output about the current time, number of days your system is up, number of logged-in users etc.
If you'll enter this very same command into the terminal in capital form as
UPTIME, you'll receive a more readable summary of the logged-in sessions by the user.
The same output can be given by entering
w command into the terminal.
Do remember you will always have a minimum of 2 logged-in users. By default when you open another terminal session it will be counted as another active user logged in. In other words, if you open four-terminal sessions, you will see 4 users logged in +1 as the default logged-in user I have written about.