For the characters in Dragon Ball Z: Kakarot, training is a lifetime commitment they are more than happy to do. The warriors are more than willing to find ways to test themselves and push beyond their limits. A way you can do that in the game is following the Turtle School Training guide, and completing the various tasks inside of the manual.
To find the massive list of tasks available in the Turtle School Training guide, you need to head to the main menu and then go to the story section. Click on it, but you won’t find it in the extensive main or side story mission checklist. You need to tab over to the left to view the manual. You can see how many tasks you have completed and how many you left to do. However, these are not all of the tasks.
You need to visit Master Roshi on his island at Kame House periodically. You want to check back in with him regularly to turn in missions and gain new pages for the training manual. These tasks vary from locating different colored orbs, creating link bonuses in the community board, playing the game for a set amount of time, or increasing a particular character’s level. Unfortunately, you won’t be able to grab any of these missions during the Namek Saga because you’re on Namek, but when you return to Earth, make sure to speak to Master Roshi.
To gain the Turtle School Legend achievement, you want to finish 50 of these training challenges. The crucial bit to remember is you need to speak to Master Roshi or none of your completed training tasks and you won’t be able to grab more.