BB-8 is an astromech droid that moves on a rotating ball in Star Wars: The Force Awakens. Carrying part of a map that leads to Luke Skywalker, he is forced to part with Poe Dameron, his master and close friend. He travels across the deserts of Jakku in order to keep the map out of the hands of the First Order.
Accompanying Poe Dameron on Jakku, BB-8 meets Lor San Tekka and receives a data chip containing the whereabouts on the lost Jedi Luke Skywalker. However, the village they are in is discovered and attacked by Kylo Ren and several Stormtroopers of the First Order. When Poe's ship is damaged while attempting to escape, Poe stays behind to protect the villagers and sends BB-8 away from the battle with the information in tow.
BB-8 eventually meets Rey, who reluctantly lets him tag along with her. When the First Order returns to Jakku searching for the map, the pair escapes with Finn in the Millennium Falcon. Finn confides with BB-8 over his past affiliation as a Stormtrooper and convinces BB-8 to direct them to the Resistance base. The group run into Han Solo and Chewbacca, who take them to Takodana. There, Rey and BB-8 discover the lightsaber of Luke Skywalker. Upon touching it, Rey becomes frightened by a vision and runs off into the wood, with BB-8 following her. The First Order attacks shortly after, prompting Rey to have BB-8 leave her to avoid being spotted. Following the Battle of Takodana, BB-8 returns to the Resistance base on D'Qar and is reunited with his master. He eventually finds an inactive R2-D2, curious over the latter's current condition and wondering if R2-D2 had the rest of the map in his backup memory, with C-3PO replying that it was unlikely.
BB-8 then participates in the battle at Starkiller Base, accompanying Poe on his X-Wing. After the battle, the two return D'Qar. Upon arrival, R2-D2 awakens and reveals that he had the map to Luke's location, with the part that BB-8 was carrying completing it and showing where Luka was. With the knowledge of Luke's whereabouts, BB-8 and the rest of the Resistance bid farewell to Rey, Chewbacca, and R2-D2 as they set off to find Luke.
The very first concept art of R2-D2 in the early 1970s depicted him in an almost identical fashion to BB-8. However, due to technological disadvantages at the time, the creators of the movie were forced to use R2's final look instead.
BB-8 was a fully-functional prop on the set of Episode VII, with no CGI used on the character at all.