Black arrow to select a range

The ability to select an entire row with a single click is often advantageous, for example, when you want to copy an entire row somewhere else (usually to the bottom of the sheet's content). The black arrow indicates that you are about to select the entire row. It appears when you hover over a row number, and the row over which you hover will be selected on right or left-click irrespective of the currently selected cell.

So, to select a single cell in Excel, you simply click the cell. To select an entire row click on the row number. Click on the column ID in the top ruler to select an entire column. But in order to select a part of an entire row or column, in fact any other size of range, click on a single cell, hold and drag. That can be quite laborious if the range is big. Therefore there is an alternative.

From the Ribbon's Home tab select Find & Select. From the list that drops down select GoTo. In the Reference field of the dialog that opens enter the adress of the range you wish to select and press OK.

The list in the Find & Select dialog box includes recently selected ranges as well as named ranges. Your worksheet has a range named as Calculator. You can select that name in the list and press OK to select it in the worksheet. To modify or delete that name use the Name Manager accessible from the Ribbon's Formulas tab.

This time I noticed that the first cells in all used columns of your worksheet have Data Validation. The designer of that sheet used the feature not to restrict entry but to create an alternative to Help Tips. I think that is a smart idea which I shall remember. Help Tips are a feature of UserForm controls (such as Text or Combo Boxes). They can be used to tell the user what is expected of him. When used in the way demonstrated in your worksheet Data Validation enables the feature for every cell. Great!