The class hall how do I do national quest?

To do a national quest Tap on the class hall building and choose the national quest option. There will be many missions to choose from in the various buildings (select the building at the top). You must find a mission that matches your class and to begin with it will need to be a level 1 mission.

Missions run for different amounts of time from 1 hour to 5 hours. The longer the mission the more Exp you will earn. Send to the longest one you can. At the bottom of each buildings list is a team mission. Up to 3 can join these and you get more Exp for more people. But everyone must join within 30 minutes of the first person.

Earning Exp lets you unlock cards in the class manual option. Once unlocked you can then use some of these when starting mission. (and the others in the class manual). When you select a mission tap the 'Select Card' button to add any of the bonus cards you have unlocked to get better rewards.