Duel Links is holding a series of rewards and events for the arrival of Duel Links on home PC, and this is the main one.
Duel constantly to fill your gauge. The more you Duel, the more the Duel Meter gains Bonuses.
The Key Reward is the Spell Card, Quick Booster, which works with cards like Magical Something.
Though most of the Daily Meter is earning Gate Keys, Gold and Gems.
While the Daily points are meant to accumulate between Gold and Gems with the key reward being, as mentioned, Quick Booster.