You pick a type - light (think Krillin as that type specializes in manipulating ki and speed), heavy (think Nappa with the power or Broly), or normal (think Goku who can learn the most techniques for his body type and has best balance of power and speed)
You then train with your master, mines was Krillin over Tien. You have to complete 60% of training with each master before you can change masters. I did 80 something with Krillin whose training gets harder as he bring in Gohan, Piccolo, and Goku for sparring sessions. At the end he taught me Kamehameha, gave me his fight type capsule which boost energy attacks, and added to my ki bar.
Then I found Ginyu (had the force train you in one session) and later 18/17 (if you get th game and fight them know they can double team you) on the map. After you beat them they offer to be your masters and give you dragon balls. The androids also give you the radar. I did 60 percent with Ginyu and he helped my d mostly. Then I trained with 18 who was really good at showing you combos and counters; finished 60 percent with her too. I also got a new technique from her.
Your power, health, defense, and other levels all build up as you train and fight.
The radar is a help as you can see clothes, hair, logos, battles, and balls on the map. Scouters are also nice as they can read powers from a distance in free roam and you can follow them. Nimbus is just a touch of dragon ball
I met Piccolo in battle and then he pushed me into becoming a SSJ by using the anger trigger like on the show. He gave me a ball, told me about omega Shenron, and offered to train me as well as unlocked the possibility to train with Goku, Gohan as a kid and teen, and
Also unlocked Majin Vegeta and Ultimate Gohan as possible masters