Welcome Caliista!
As others mentioned social guilds and communities are a good way to go usually.
Open World and Instances are kind of rarer possibilities, but they exist. Did find myself two people that I play a lot with and we support each other. The problem here its “by chance”. So the first option would probably be more effective.
You can also take a look into:
https://eu.forums.blizzard.com/en/wow/t/post-if-you-want-to-make-some-in-game-friends-pt3
Welcome again and enjoy 
For Azeroth!