connecting two people over the Internet

I am busy making a 1v1 multiplayer game, but i have no idea how to connect two computers with each other over the internet. I saw some tutorials on Youtube, but none of them showed how to do it over the internet instead of inside a single computer.
Does someone know the answer?

Greatings and thank you!

Is this maybe possible with RakNet? and if so, what do i need to achive this (one or more servers etc)