There are three different ways to set your font styles for the content pages within your web site.

To apply fonts globally for all your pages:
Website Design > Content Window > Fonts

For a single page:
Website Controls > Manage Pages & Galleries > Click Edit beneath the appropriate page > Page Design Tab > Page Fonts
This will override the global font settings above.

For sentences or words within a Text Asset on a page:
Website Controls > Manage Pages & Galleries > Click Edit beneath the appropriate page > Page Content Tab > Edit Current Content button > Use the text editor tools
The text editor will override the both the page and global settings above.

Related article: Working with page backgrounds