Excel gives you a choice between editing a cell's contents in the cell or on the Formula bar. Whereas, most of the time, editing right in the cell is just fine, when dealing with really, really long entries (like humongous formulas that seem to go on forever or text entries that take up paragraphs and paragraphs), you may prefer to do your editing on the Formula bar.

Editing on the formula bar is easier because Excel expands the Formula bar to as many rows as are necessary to display the entire cell contents, whereas, in the worksheet display, the cell contents may be running right off the screen.

To edit the contents in the Formula bar rather than in the cell itself, you must position the cell pointer in the cell and then double-click somewhere (probably the first place that needs changing) in the cell contents on the Formula bar.