When a new player joins an established game, it's important to bring them up to speed with the story so far. Normally this would be the job of the GM, speaking out of character. But to really get the new recruit into the roleplaying spirit, try delivering the background in character, through the other players.
Some players might even be eager to share their adventures. Just keep an eye on them so that you get some actual new adventure into the session.
C-3PO: About twenty years ago, we helped save the Galactic Republic from a war instigated by Separatists.
C-3PO: They stole the Lost Orb of Phanastacoria from a peaceful planet called Naboo, and blew up their moon with it.
C-3PO: The Chancellor of the Republic, Palpatine, designed the Peace Moon to replace it, but the Separatists discovered it had a secret defensive laser in it.
C-3PO: They stole the plans and started building one of their own, to power with the Lost Orb and use as a weapon.
C-3PO: Our former masters, Senator Amidala and her husband Anakin, may they rest in peace, stopped the Separatists and ushered in an age of peace and prosperity.
C-3PO: The public loved Palpatine so much that they declared him Emperor for life. But he's beholden to the corrupt Senate.
C-3PO: We're part of a Rebellion against the Senate. Recently we uncovered clues that the Lost Orb is inside the Peace Moon.
C-3PO: We can't let the Senate have a weapon capable of destroying a planet.
C-3PO: We stole a copy of the plans so we can locate the Lost Orb, take it, and return it to the rightful owners, the Gungans of Naboo.
C-3PO: Without the Orb the moon will truly be a Peace Moon.
Adam: Can I replay this cut scene later?