The problem with fonts is that the only fonts web designers can use are those on the surfer's computer, and there is no standard set of fonts that everyone has. Most web browsers default Times New Roman or its equivalent as the font for a web page. If the text has been preformatted (using the <PRE> tag) most browsers default Courier New or a similar font.
You can specify a hierarchy of fonts in both HTML and CSS (the syntax is different in each) to control they overall style of font that displays. For example, a hierarchy of "Futura, Arial, Helvetica, Sans-Serif" would make the browser use Futura if it's available; if not, it would try Arial; if Arial was not available the browser would look for Helvetica, finally searching for any Sans-Serif font on the system. Unfortunately there are significant differences between these fonts in size and style, and this type of system will not help you if you want to use a less common font like Mistral.
Most web designers have abandoned use of fonts in HTML and instead used GIFs to ensure that everyone sees the right font. Some companies like Microsoft have released free fonts that look good on the web. The problem is that until everyone (or at least most of the people visiting your site) have installed those fonts, you can't be sure that fonts alone will work.