For daily challenge, players have to collect the given alphabet words in-game process in order to complete the daily challenge.
As shows in above picture, players have to collect the word GOAL. While playing, the alphabet will come out in sequence like G-O-A-L and the players have to collect all of them to complete the daily challenge.
Players have 24 hours to complete the given daily challenge and once completed players will rewarded a mystery box. If the player din't manage to complete the daily challenge, no reward will be awarded and the daily challenge will refresh a new word once the time ended.
For Mission, players have to complete all the given task in order to increase the score multiply. Once the one of the mission completed, a tick will be place as complete else the mission will show the remaining amounts to go.
As for the missions, it will never be refresh or disappear unless player decide to spend coins to skip the mission as shows in below picture.