The film depicts the fate of Goku and Vegeta as they encounter a new Saiyan called Broly. In the manga, it is said that Frieza once again caused trouble though it's a tale for another time. Nevertheless, the two Saiyans emerged from the conflict even stronger than they were before.
This is the second saga in the Dragon Ball Super manga to have been skipped. The first being the Golden Frieza Saga - which was also only featured in a few panels to indicate its events. Interestingly, both sagas involve a heavy focus on Frieza's empire's inner-circles.