Microsoft EXCEL - Fill Handle

Instead of entering data manually on a worksheet, you can use the Auto Fill feature to fill cells with data that follows a pattern or that is based on data in other cells.  You can also copy formulas from adjacent cells to save reentering the same formula into several cells.

To do this, position mouse cursor on bottom right corner of cell you wish to copy or begin a pattern.  Once you have the bold plus symbol, left mouse click and drag down to the cells you wish data or formula to be inputted in.  You can also double click rather than drag down - data entry will stop once an empty cell is located.

In the above example drag the fill handle down from each cell reference to create a series as shown below.

See how column A simply copied the numeral 1 down.  To count 1 2 3 4 etc. Input 2 in cell A2 then select both A1 and A2, then move the mouse cursor to corner of cell A2 to get the fill handle, then drag down.  Excel will then input 3 into A3, 4 into A4 etc. 

Alternatively,  you can fill the active cell with the contents of an adjacent cell by selecting an empty cell that is below, to the right, above, or to the left of the cell that contains the data that you want to use to fill the empty cell. Then on the Home tab, in the Editing group, click Fill, and then click Down, Right, Up, or Left.