Attuned is when you can go through the door and skip the YR to go straight to GR. To be attuned takes lots of time-as you need to go through YR, GR to get to the 100% room and see Kamila. As well as get a 100 minion quest. Once you finish the 100 minion quest, you are attuned.
There are people who do attunment runs. Advice would be to get to at least an 11.4-11.5 before worrying about it(I got attuned at an 11.4 with Dark Runner).
I see! Thank you! Oh and when people shout for tuna runs.. does that mean they're helping people get attuned or are those for the attuned people?
A tuna run is the former, a run whose primary purpose is to help people become attuned. They run through the ym as fast as possible (usually without suppressing to 11.4), work through the gm and the hpr, and listen to Kamila's speech. Whether they actually kill her first form is optional.