I am level 90.
In the blasted lands I met Khadgar and he said "Are you prepared to face whatever's on the other side of the portal?" and I felt that I was ready, after that I have a choice to embark on a dangerous mission, I want to go but there is a warning about not being able to return immediately.
What exactly can I not return to?
Best Answer
Azeroth. What he's talking about is that after you cross through the Dark Portal, you have to play through a (roughly hour-long) introductory quest chain before you can leave. Shortly after you complete the intro sequence, you should acquire the means to return to Azeroth.