From Project main menu

An easier way to add task to a project is from the New task option from the main menu. 

1. Click on Add > New Task from the main menu.
2. Select the appropriate option so that you can pick the project where the task needs to be created.
3. This will open an Add Task pop-up where you can specify the details of the task.
4. Click on Save. The task will be created in the project.