For all but the most simple projects, it is helpful to arrange the tasks in your project into some sort of groups. In Project, these groupings can be created with something called a summary task .
To make a task into a summary task, you must indent the task below it. Hover the mouse pointer over the left edge of the task name of the task below the task you want to make into a summary task.
Hold down the left mouse button and drag it to the right. A vertical line appears indicating how far you are indenting the task.
When you have indented to the desired level, release the mouse, and the task above the one you were dragging will now be a summary task.
IMPORTANT Select the task and then click the Indent toolbar button on the Formatting toolbar.
When working with tasks that could be made subtasks for several different tasks, pay close attention to the position of the vertical bar. If the mouse was released at this point, Task Three would become a subtask of Task One.
However, if the mouse pointer is released here, it would become a subtask of Task Two.
To make a task into a summary task, you must 
Hold down the left mouse button and drag it to the right. A vertical line appears indicating how far you are indenting the task. 
When you have indented to the desired level, release the mouse, and the task above the one you were dragging will now be a summary task. 
When working with tasks that could be made subtasks for several different tasks, pay close attention to the position of the vertical bar. If the mouse was released at this point, Task Three would become a subtask of Task One. 
However, if the mouse pointer is released here, it would become a subtask of Task Two. 
