Every day when you log in to the game, you can claim a daily bonus in the Special Events tab on the main game screen:
There you will find a calendar with different rewards. Their number varies by the number of days in the month. Also, some of them will be doubled if you have reached the required VIP level.
Daily bonus refreshes every 24 hours at 5:00 AM your in-game time.
Rewards are not assigned to specific days of the month. If you miss a day, you can claim a bonus starting from the day you have missed. However, you will not be able to collect the last reward of the month.
Note: The daily bonus calendar restarts at the beginning of every month. Hence, in February, you will get only 28 or 29 rewards.