This is taken from Disney Wiki:
The story revolves around the protagonist Jack, who fell in love with a higher merchant class, Angelina. However, Marco, a noble who loved to travel (based on Marco Polo), was part of the love triangle. They also met Inma, a tomboy teenage girl who fought for injustice, but was never taken seriously due to her age.
The humans made a pact with a family of Thunder Giants: Feebus, Fifen, Fogel, Fobert, and their leader, Faustus. They were villains with a relatable point of view. The humans agreed to give the giants a percentage of their harvest and livestock, they'll prevent any danger that might befall the humans. However, as time passed, the giants seemed to forget their duties often, making the humans miserable and doubting the pact.
One day, Jack ended up befriending a giant, which started an adventure.