Invasions are so hopelessly confusing. I understand the concept but, I don't understand how to do them. People say you can grind via them but, how? All the groups Is see are doing WQs and nobody wants to explain shit to me. I ask and they insult me in-game. Like literally why is it I get a thousand different answers but, no solution?
Can you see the WQs on the map? It will look something like this if you can:
If no: you can't do anything with the invasions yet. You have to unlock world quests first, which require hitting 110 and a light rep requirement (IIRC friendly with the four main zone factions in Legion). You only have to do this once on your account, and then it's unlocked automatically for your other characters.
If yes: then you go to the icons on the map and complete the objectives, much like the bonus quests from Draenor that you may be familiar with. At 110, there is also a meta quest to do 4 invasion world quests that is automatically granted to you when you zone into the area, and that leads to a scenario which wraps up the invasion.
When people talk about grinding, they likely mean just doing the six WQs on a low level character, as it can be decent XP for the time invested (and really good XP for those with flying unlocked).
I've seen you bring this up a few times now and people have provided similar answers, so I'm trying to figure out exactly where the disconnect is so we can explain further if we need to.