First thing to do:
Boot to INTERNET recovery.
This is NOT THE SAME as "the recovery partition".
Command-OPTION-R
at boot.
If you're connecting via wifi, you'll need your wifi password.
The internet utilities take a while to load, be patient.
Once the utilities are loaded, open disk utility.
VERY IMPORTANT VERY IMPORTANT:
Go to the "view" menu and choose "show all devices".
You can now see all drives, volumes, containers, etc.
Since this is a "brand new Mac" (to you), I would erase the internal drive, then re-install the OS.
Do it this way.
Look at the list on the left (you did select "show all devices", right?)
The topmost item should represent the PHYSICAL DRIVE inside the Mac.
Click on it and click "erase".
You want "APFS with GUID partition format".
When the erase is done (shouldn't take long), quit disk utility.
Open the OS installer and begin "clicking through".
The Mac may restart one or more times, and the screen may go dark for a couple of minutes with no other indication of activity. BE PATIENT.
When done, you should see the initial startup screen (choose your language).
Just go on from there...