New players of course don't know the detailed back-stories of events, characters, and objects within an ongoing campaign. But rather than tell them all about it or hand them a dossier when they join the game, having them learn things organically during play is both* easier, more realistic, and ultimately more satisfying.
And provides opportunities for byplay when they figure out and state with amazement something that everyone else already knows.
* Yeah, we know. There should be a single word in English that means "all three of".
GM: Good work. You've escaped Jabba's clutches.
Chewbacca: Not that Jabba had clutches...
Lando: So, Han, old buddy. What... exactly... were you aiming at when you shot that blaster?
Han: Does it matter?
R2-D2: I scan the wreckage for the Lost Orb.
GM: You don't detect it.
R2-D2: We have to go back to Jabba's palace.
Chewbacca: We should scan it from the Falcon. No need to risk going in there needlessly.
R2-D2: Mmm. Good idea.
GM: Just to wrap this up, when you do, there's no trace of it.
Luke: Wait, that's funny. We've lost the Lost Orb! Get it?
Leia: Yeah, by now it's the Lost, Found, Lost, Found Again, Lost Again Orb. Of Phanastacoria.
Luke: Where is Phanastacoria?
C-3PO: That's lost too.