So this is probably getting outside the scope of this forum - more suited for the Netlify forums, or a general networking forum…but I’ll give it a go by way of analogy.
The church I attend is legally called ‘Crown Road Presbyterian Church’. That’s the name of the bank accounts etc. However, everyone calls it ‘Gympie Presbyterian Church’ (Gympie is the name of the town/city it’s in) because it’s the only Presbyterian Church in the town, and Crown Road is meaningless for most people.
So, if someone says ‘take me to Crown Road Presbyterian Church’ or ‘take me to Gympie Presbyterian Church’ on a Sunday, they’ll end up at the same location. However, when they get to the building, no matter what name they used for directions, they’ll see the words ‘Gympie Presbyterian Church’ written everywhere.
Your site is similar.
There are two ‘names’ (URLs) you can call it by. You can ask your web browser to take you to either URL, and since URLs are resolved to IP addresses, they’ll end up taking you to the same website (i.e. the same HTML, js, and css files will be delivered to your browser). Depending on the code you’ve used to build your website (for this situation, the code built by hugo using your configuration file) any link which uses .Site.BaseURL or anywhere that .Permalink appears in your layouts, will have in the resulting HTML whatever you’ve set as baseURL in your configuration file. Back to the analogy - no matter which name you use to get there, the building will have the same sign on the side.
Does that help?