Excel's AutoFill feature is a powerful tool for quickly filling a series of data, be it numbers, dates, or even text with a specific pattern. Here's how you can use it:

1. Enter the Starting Values:

- For numbers: Enter at least the first two numbers in your sequence. Excel can identify the pattern and extend it. For example, if you want a sequence increasing by 2, enter 1 and 3 in the first two cells.
- For dates: Enter the starting date in the first cell.

2. Select the Cells to Fill:

- Click and hold on the bottom right corner of the cell containing your first value (the fill handle). This is a small black square that appears when you hover over the corner.
- Drag the fill handle down (for numbers or dates) or across (for filling text in a series) to select the range of cells you want to fill with the series.

3. Observe the AutoFill Options (Optional):

As you drag the fill handle, a small box might appear near the corner of the selection. This box shows how Excel interprets the pattern in your starting values.

- For numbers: It might show "Linear" if it detects a constant increment or decrement.
- For dates: It might show "Days" or "Months" depending on the difference between your starting date and the cell you're dragging to.

4. Choose the AutoFill Option (if needed):

- If Excel guesses the pattern correctly (e.g., "Linear" for adding 2), you can simply release the mouse button to autofill the series.
- If Excel doesn't guess the correct pattern, click on the small box to see additional options. You can choose "Copy Cells" to simply copy the first value, "Linear" to fill a numeric series, "Dates" or "Weekdays" to fill dates based on your starting point, or "Fill Series" for more advanced options like filling days of the week.

5. Fill the Series:

- Once you've chosen the appropriate option (or if Excel guessed it correctly), release the mouse button, and Excel will fill the selected range with your data series.

Additional Tips:

* To double-check the series or change it mid-fill, you can edit any cell within the filled range, and Excel will adjust the entire series based on your changes.
* For more complex series (e.g., alternating numbers), you might need to enter more than two starting values or use the Fill Series option within the AutoFill dropdown for more control.

By using AutoFill effectively, you can save time and ensure consistency when entering repetitive data sequences in your Excel spreadsheets.