In a project, you have the possibility to assign multiple tasks to multiple team members.
Choose from the menu Projects and select your project from the list:

Click on the TASK BOARD tab:

Select a task list, so that all tasks in this list will be selected. The multi-selection menu bar will appear. The menu bar will also display how many tasks have been selected.

Click Edit and the following Mass edit tasks dialog box will appear:

In the Assign to project members field, select your team member(s) and click Save.

All tasks which were selected have now multiple project members assigned to them.
