Q. I notice that each word in the toolbar has one underlined letter. What is the significance of this?

A. Those underscores are very useful because they give users an alternative way—without the mouse—to activate many commands. You access the commands directly from the keyboard. If you hold down the Alt key while pressing a keyboard letter corresponding to one of the underlined letters in the toolbar, it will trigger that command in the menu. For example, notice that the word Format has the letter “o” underlined. If you hold down the Alt key and press O (not the numeral 0) on the keyboard, the Format menu drops down. And then, if you want to activate one of the commands in the Format menu, keep holding down the Alt key and press the underlined letter in the menu list.

The underlined letter convention is not limited to Word. It extends to many Windows applications—not just Microsoft. And it’s a handy shortcut.