A clarification on the Gateway and Clients tab.

[WhiteTiger-IT]

I need two clarifications on configuring OpenVPN.

If user "John" doesn't need to log into pfSense, does it still make sense to create it in System/User Manager? Or maybe it's better to create a profile in the Clients tab.
If I create the user in FreeRadius, how do I associate it with a new Client?

I used the Wizard to create OpenVPN.
Now the user "David" (created in User Manager) is able to connect to all what is on the LAN and the DMZ, without my having changed anything in the various configurations of pfSense.

I see there is the default rule in the Firewall/Rules/OpenVPN.
I see that an ovpns1 interface has been created, yet to be assigned.
In the doc it says that if I assign this new interface, a Gateway will also be created and a new tab in Firewall/Rules.
What I can't understand is what this gateway is for and what rules to foresee.

Thanks in advance for any help.