Any material longer than a single character (or cell) in your document must be selected in order to be cut, copied, or deleted. This is done with the Highlight command.
On the Macintosh, the Highlight command does not appear on the Edit menu, but it is still available to you. To begin highlighting, move the cursor to the beginning (or end) of the material to be selected. Then you can either click-and-hold the left mouse button and drag the cursor over the area to be selected, or you can hold down the Shift key and use the Arrow keys.
In fact, while holding down the Shift key, the Arrow keys (Up, Down, Left, Right), the Home and End keys, and Page Up and Page Down serve to move quickly through a line, sentence, or other block of text, highlighting as you go.