1. Copy formulas: When you drag the fill handle down or across a column or row, the formula in the original cell is copied to the other cells. The formula may be adjusted automatically to reflect the new cell references, depending on the type of formula and how it's written.

2. Continue a series: The fill handle can also be used to continue a series of data, such as:

* Numbers: For example, if you type "1, 2, 3" in three cells, dragging the fill handle will continue the series with 4, 5, 6, and so on.

* Dates: You can create a series of dates by typing the first date and dragging the fill handle.

* Days of the week: Similar to dates, you can create a series of days by typing the first day and dragging the fill handle.

* Text: The fill handle can also continue a pattern in text. For example, if you type "A1, A2, A3" in three cells, dragging the fill handle will continue the series with A4, A5, A6, and so on.

How to use the fill handle:

* Select the cell(s) containing the formula or series you want to continue.

* Hover your mouse over the fill handle (the small square in the bottom-right corner of the cell).

* Click and drag the fill handle in the direction you want to copy the formula or continue the series.

The fill handle is a very handy tool for quickly copying formulas and continuing series in Excel. It can save you a lot of time and effort.