Your site comes with a rich-text editor which functions as any standard word processor might. The term "WYSIWYG" stands for "What you see is what you get" meaning that changes you make in the text editor area will appear as they would on the page itself.
There are options for bold, italic, bulleted and numbered lists and more. Most of these you'll recognize from word processors. These are used in the same way you'd expect. Select the text you want to change, click the button and it will be bold, underlined, or change font color for you....
Read more about Overview of the Text Editor (WYSIWYG)