Add Task from Gantt

From Interactive Gantt: 

1. Go to your project. By default, you are taken to the Interactive Gantt. If not, click on the Interactive Gantt from the views.
2. From the Gantt menu bar, Click on the Add option and then click on Task. 
3. This will add a new task in your project plan. 
4. Enter your task details and click Save.

You can also add sub-tasks, Milestones, Predecessor, Successor, etc. from here.
 

Add Multiple Tasks:
At times when creating your WBS, it is more convenient to add multiple tasks in one go. With this option, you can easily create your WBS with task names or go with adding other details such as resources, dates or duration at the same time. To do this,

1. Go to the Interactive Gantt view of the project.
2. Click on the Add > Multiple. 
3. This opens a popup where you can enter task name, resources, Start/Finish dates, etc and click Submit. 
   

Some rules to remember:

1. If Both Start and Finish dates are specified, then the task created is manually scheduled.

2. If Duration is specified, then the task created is auto scheduled.

3. If system cannot determine the schedule mode from what the user has entered, it will use the user’s preferences to create the task.