The Create multiple tasks link can be used to create several tasks at once. For example:
Another method is administrator users can import data via Tasks > Import Tasks. This method requires you to upload an Excel CSV formatted document with your task data in it. For more details on this, just follow the steps in the import procedure.
Lastly, the API can be used to import tasks. Any developer familiar with RESTful API should be able to build an integration. More information about the API can be found here.