On the main screen press RB (twice) to open the daily Adventure Board. There will be three adventures, each adventure having three battles (edit: some adventures might have 4 battles, some might even have 5).
Win all the battles and you unlock the achievement.
Only the daily adventures are needed. There is another task that does not reset every day (like kill 100 troops etc.) which does not need to be completed for this achievement.
The battles themselves are not difficult, but it depends on your team. Players who have just started playing the game might have trouble winning some of the more difficult battles. If that is the case, just wait for another day's adventures. They might be easier for you.