A great deal of story takes place between the end of the Naruto series and the start of Boruto: Naruto Next Generations. The true conclusion to the Naruto story ends with a second bout between Naruto and Sasuke at the Valley of the End, with the title character marginally coming out on top and a reformed Sasuke setting out on a journey towards redemption. The loose ends of the Fourth Great Shinobi war are tied up, Kakashi is appointed Hokage and a memorial is held for those who lost their lives during the final arc's hostilities.
An epilogue follows, set fifteen years later, and serves to set up the Boruto story. Clearly, much has changed during this period. Naruto has finally become Hokage, the audience is introduced to the children and relationships of the main heroes and peace still reigns over the ninja villages. The modern version of the Five Kage is also revealed as Naruto, Gaara, Chojuro, Darui and Kurotsuchi. Naruto's epilogue gives a brief snapshot of Masashi Kishimoto's updated ninja world, and this period is somewhat explored in The Last: Naruto The Movie, but many salient details of the time skip aren't explored until much later.
Perhaps the biggest of these is how far technology develops over that fifteen-year period. The epilogue depicts a new Konoha, complete with modern skyscrapers and recognizable conveniences such as portable games consoles and laptops. However, the ninjas' tech revolution goes far deeper. Konoha establishes a science division and begins fusing chakra and ninja techniques with engineering, inventing tools such as sonic flash bombs and boots that allow ninjas to climb trees and walls without using their chakra. This development likely came about as a result of Kishimoto's desire to delve into the science fiction genre, which has since inspired the author's new series, Samurai 8.
The full consequences of these developments aren't revealed until deep into the Boruto story. Due to the enduring peace and increased commerce, Konoha Village, which seemed almost entirely populated by ninjas during Naruto, is now predominantly civilian. Ninjas have not only lessened in number, but have become weaker due to a lack of genuine combat experience and this creates some cracks in the political landscape. Several enemy factions appear, either intending to trigger a return to the old days when ninja were stronger, or seeking to take advantage of the lack of new warriors for power and profit.
Many of these criminals pale in comparison to actual ninja, but one powerful group began forming in the shadows during this fifteen-year period. Going by the name of Kara, a member of the Otsutski clan known as Jigen started assembling a team of ninjas and providing them with technological enhancements. Kara would also begin to reach out to the wider world and establish a network of spies that includes heroes from the Naruto series, such as the Hidden Mist's Ao, while also infiltrating Konoha's science division.
Thankfully, several major Naruto characters return in Boruto having learned powerful new techniques off-screen. Devoid of his Sharingan eye, Kakashi now uses a move called Purple Lightning, while Sasuke masters his Rinnegan eye to freely travel through portals in space.
As for old foes, Orochimaru's contribution to the Fourth Great Shinobi War earns him a pardon from Konoha. The snake Sannin lives in the forest with Karin, Suigetsu and Jugo under constant guard by Yamato, attempting to create a synthetic child called Mitsuki, while Kabuto takes over the Konoha orphanage. The villainous Danzo, leader of the Root division, remains deceased but his will lives on during the fifteen-year time skip, and a beast made by Root from the cells of the First Hokage is implanted into Sumire Kakei, a future classmate of Boruto's.
Boruto: Naruto Next Generations continues June 30th on Adult Swim.