Explanation

Excel can automatically create an outline when the worksheet contains a suitable summary structure.

Go to:

Data → Group → Auto Outline

Excel analyzes the data and creates groups where possible.

Outline Levels

Excel may display outline buttons such as:

1 | 2 | 3

These levels allow you to control how much detail is displayed.

Example

Level 1: Summary only
Level 2: Summary + major details
Level 3: Full detail

Practice

Create a sales report with monthly details and totals, then try:

Data → Group → Auto Outline

Review the generated outline.