Excel gives you the opportunity to make some characters stand out from others with the familiar "styles" of Bold, Underline, and Italics. The process for converting text to one or more of these styles is to select the cell(s) and click on the appropriate button. The style buttons function identical to many Word Processing programs.
The example below should give you an idea of the visual effect that might be achieved with one of these styles. (There will be some visual differences depending on the font and size you are using in how the styles are displayed.)
Excel provides three buttons to make the style change easy to reach. Once a style has been applied, you can click on the cell with the style and click on the appropriate style button to remove the style formatting. Hover your mouse over the different style buttons to get a reminder of which is which.
Note that you can apply combinations of styles. That is, you can have bold text that is also underlined. An underlined word also may be viewed in italics.