Starting from level 3, you will receive daily gifts upon entering the game. They can contain coins, diamonds, energy, and other useful items such as growth elixirs.
(the daily gift window)
The bar at the top of the window shows your progress towards the next login gift - you get them on days 8, 15, 22, and 30. This login streak does not reset if you skip a day.
The cards at the bottom are daily login rewards. Each one is more valuable than the previous one, and your streak will reset if you miss one. Make sure to log into the game every day to claim them all!