Namek

Trunks-"Alright you two ready were going to planet Namek, were gonna get the dragon balls to tell us where supreme kai is."

Gren-"Dragon balls?"

Lilly-"I'll tell you later, in the meantime we should train on our way there."

Trunks-"there is a gravity room in the ship, you guys can use it all you like."

Gren-"...okay?"

Lilly-"Lets go no time to lose."

On your way there Lilly explains what the dragon balls and the gravity room is

Gren-"Really, huh wish orbs and a super effective way to train, sounds unreal."

Lilly-"Yeah."

After you get into the ship the journey starts.