The hard journey to find Luke Skywalker
More than 30 years after the destruction of the Second Death Star, Luke Skywalker, the supposedly last surviving Jedi knight, went missing. The First Order has emerged from the ashes of the Galactic Empire, and is looking to destroy the New Republic. The Resistance, a Republic-backed fighting force, under the leadership of General Leia Organa, tries to search every corner of the galaxy for Luke - who is beleived to cast the twist to battle between the two sides.
In a village on the planet Jakku, a Resistance pilot named Poe Dameron meets an old man to get a map showing Luke's location. The stormtroopers under the command of Kylo Ren land soonly and destroys the village before capturing Poe alive. His droid, BB-8, escapes with the map hidden in its memory cabinet.
The main storyline of "The Force Awakens" is a race between the First Order and the Resistance to obtain the piece of the map (actually a USB containing data) about Luke's position in the galaxy.
Rey
Being a girl picking up scrap to earn a living, Rey stumbles upon droid BB-8 and then Finn (known as the betrayal stormtrooper FN-2187) and is dragged into the current war scene. They rob a ship parked nearby to flee the planet when the Stormtroopers hunt them down, without knowing that ship is the legendary Millennium Falcon, and thus later meet Han Solo and Chewbacca.
On the planet Takodana, Rey finds a cellar and comes across the lightsaber of Anakin Skywalker. She quickly senses mysterious hallucinations, but refuses to accept it at Maz's suggestion.
In the ensuing developments, Kylo Ren's continuous chasing of Rey forces her to use the the saber and unleash the gifted power, actually the Force, hidden within her.
Han Solo and his son Kylo Ren
Ren is the son of Han Solo and Leia, originally named Ben Solo, and was once one of Luke's Jedi disciples. He is succumbed to the dark side of the Force, initiated by the First Order supreme leader, Snoke, and helps the villian destroy Luke's Jedi Academy. This is the reason why Luke decided to go into seclusion.
In the movie, Han tries to advise Ren to return to the light side but is killed by Ren on Snoke's command.
The Millennium Falcon spaceship
After Han Solo's death, Rey seems to become the new owner of this spaceship. At the end of "The Force Awakens", she and Chewbacca fly the spaceship to the planet where Luke is reclining, following the instructions of the completed map.