When you open a new workbook, the first cell is the active cell. It has a black outline. In the second picture, cell C5 is selected and is the active cell. It is outlined in black.
Cells are where you get down to business and enter data in a worksheet.
When you open a new workbook, the first cell you see in the upper-left corner of the worksheet is outlined in black, indicating that any data you enter will go there.
You can enter data wherever you like by clicking any cell in the worksheet to select the cell. But the first cell (or one nearby) is not a bad place to start entering data in most cases.
When you select any cell, it becomes the active cell. When a cell is active, it is outlined in black, and the headings for the column and the row in which the cell is located are highlighted.
For example, if you select a cell in column C on row 5, the headings on column C and row 5 are highlighted, and the cell is outlined. That cell is known as cell C5, which is the cell reference.
The outlined cell and the highlighted column and row headings make it easier for you to see that cell C5 is the active cell. Also, the cell reference of the active cell appears in the Name Box in the upper-left corner of the worksheet. By looking in the Name Box, you can see the cell reference of the active cell.
All of these indicators are not too important when you're right at the very top of the worksheet in the very first few cells. But when you work further and further down or across the worksheet, they can really help you out. Keep in mind that there are 17,179,869,184 cells to work in on each worksheet. You could get lost without the cell reference to tell you where you are.
For example, it's important to know the cell reference if you need to tell someone where specific data is located or must be entered in a worksheet.
In the practice you'll see how to use the Name Box to go straight to cells located anywhere on the worksheet.