It's different for "everyone" (provider, operating system, ethernet card...).
But I'm sure your favorite search engine will find a website that explain it for your case.
I see that on my "personal account" on my provider website : I have access to my modem's settings.Note : if you play on a public connection (hotel, airport, school, work...), the network manager probably closed those ports : there are "games" ports.
Can ask him to re-open them but... it's not always a good idea
("Hi boss, I want to play a game instead of work, can you ask the tech' to re-open gaming ports ?
")
Note2 : pay attention to "free ports test " on the web, they said all my ports are closed (... I have maybe a magical connection and don't need to be connected to use the Internet
... in fact it's just because Windows block these tests)