Those who Glimmer are highly susceptible to the broadcast dreams of others who Glimmer, of the Veil, and of the Dark Men. These dreams can be intensely real-seeming, to the point that an argument can be made that they are real.
"Come with me, where dreams are born, and time is never planned" - Peter Pan
In the farthest reaches of the Veil, beyond the safely overlapping areas where things almost make sense compared to the real world, one finds the Dreamscape. Perhaps they're yanked there by others who Glimmer. Or perhaps they are pulled there by Dark Men, looking to subject them to nightmares.
Dreams typically happen in the far reaches of the Veil. Near a thin point, such as Gray Harbor, the real world "bleeds through," and the Veil often takes its topography and general feeling from its real world analogy. Moving away from the thin point, however, the Veil becomes less and less analogous to the real world.
Most Dreams take place somewhere in the vast, unchartable regions of the Veil commonly called the Dreamscape. These are the places where the rules of reality can be bent and broken.
Although the term "Dream" has come to prevalence to describe these experiences, people aren't necessarily even asleep when they enter the Dreamscape.
When you experience a Dream, your body no longer exists on the physical plane. You are within the Veil and the danger is real. The pain is real, the injuries are real... and even death can be real. Those who Glimmer are far more susceptible to magical dreams; however, even those who do not Glimmer can be pulled in unknowingly.
These Dreams can be of anything. Perhaps a person is brought back into the Wild West for a gun-slinging adventure. Perhaps the dreamer is dropped into a world of fantasy, where dragons and unicorns run free. Or they are the Captain of a pirate ship, heeding to a siren's song. These can be dreams that you awaken from, feeling invigorated or at peace... or nightmares that return you to your bed, soaked in sweat and even blood.
"All men whilst they are awake are in one common world: but each of them, when he is asleep, is in a world of his own." - Plutarch
Because Dreams and the Dreamscape are really an extension of the Veil, characters can take "Veil Lore" or "Dream Lore" as a background skill to have more knowledge of Dreams.
Those who don't Glimmer rarely enter the Dreamscape, and their memories of whatever occurred there invariably alter themselves so they believe they had an intense nightmare.
Dreams are meant to be a way for you to play things a little outside the normal scope of everyday life. If you want some ideas about plots to run, check plots, where you'll find some quick ideas (and a link to a quick plot generator)!
You do not need staff permission to run a Dream.
Note that you cannot include another PC in your dreams without their consent. Even though these dreams aren't actually real, you cannot "Dream" some AU-version of someone else's character. They can only appear in a Dream if they agree to it - i.e., don't @emit a PC in your character's dreams.
Also note that these "Dreams" don't necessarily have to be something that occurs in a dream-state. Your character can be wide awake and still slip through the Veil. Perhaps something they fear or want snags them and pulls them through, in which case they simply seem to slip out of sight and sound and reach. Maybe they can find their way back on their own, and maybe they can't; how they recover themselves is up to you.