The event system consists of tasks and events. You can get many rewards which will accelerate your game progress by completing these tasks. The difference between the tasks and events are as follows:

Tasks

These will especially be helpful in developing your village at the beginning of the game. They are usually not time limited and reward you with valuable resources upon their completion.

Events

Events however, are time limited contracts that offer great rewards as long as they are completed within the time limit. They are bound to the game progress of the player to make them challenging and fun.