When you create a user story based on a template, there is a simple text field where you can enter Tasks for that user story separated by commas. When you then click the Add button to create the user story, those tasks are automatically added to the Task tab.
This should also be an option in the Excel import file when importing user stories en masse. As it stands now, there doesn't appear to be any way to include tasks when importing user stories. (I've tried adding a column with the task field name, but it generates an error when I try to import the file.) This means that after we bulk import user stories, we then have to manually open each and every story and manually add each and every task. In cases where user stories have long task lists, this can be very time consuming, and virtually negate the value of importing user stories en masse in the first place.