You can use fonts in any word processing program like Microsoft Word, Word Perfect, or OpenOffice (it's free, works on Mac and PC, and is *just* as awesome as Word! :)). You can also use fonts in photo editing programs like Paint Shop Pro, Adobe Photoshop, or the Gimp (also free, Mac & PC friendly, and a great program!).
Here are a couple articles to get you started. Pretty soon you'll be fonting like a pro! :D
Computer Journaling Basics - This informative article from Denise Gormish at Scrapjazz.com goes over the basics of using fonts in a word processing program, then printing them out to use in your traditional, paper and scissors scrapbook. :)
How to use Fonts in a Photo Editing Program - Jen Strange offers this great article on how to use fonts in Adobe Photoshop. This is a great resource if you want to use fonts in Digital Scrapbooking or to make an image using fonts and text to make, for example, a blog banner for your blog! :)