Help needed connecting database to new installation of Opencart and accessing the admin panel

Greetings:

I am writing to ask for some help installing Opencart v3.0.4.0 on my webhost.

I do not understand if it matters whether I place the software as a subdomain in my main domain (opencart3.maindomainname.com), or whether it is a better idea to place it in a common domain (opencart3.tempsite.com).

Currently I have uploaded it in my main domain (opencart3.maindomainname.com).

I should be able to build the new store in one of these before making it live, correct?

I've created a database for use with the new installation, but do not know how to link or connect it to the Opencart installation.

I surmise that needs to be done before I can access the admin panel. Is this correct?

Anything else that I am missing?

Thanks in advance!

Simply call your installation with opencart3.maindomainname.com and submit the proper db details.