Changing Fonts across entire site

I have been doing some digging and haven't been able to figure this one out. How do I change the font style across the entire site?

Thanks for the help.

It really depends on your template, what you've changed so far, etc. In a stock Zencart site using the Classic template, changing the red part here in the stylesheet would change most fonts:

body {
margin: 0;
font-family: verdana, arial, helvetica, sans-serif;
font-size: 62.5%;
color: #000000;
background-color: #e5edf5;
}

The first font in the list will be the one used for most cases. One caveat: if you use a font that isn't included in the browser (or OS) any particular customer uses, he/she won't see what you intended, so it's best to use a more common font.

The body {} rule at the top of the standard stylesheet sets the basic font sitewide; this can be overridden for any particular element or area by other stylesheet rules.
If you have a Template Monster template, everything is different. They use several major stylesheets, with completely different organization, and many of their page elements have different class or id names even when the element is in the same structure as stock.

Yeah I have the template "pain in the A55" monster template. I thought I had it figured out but it didn't change anything.

Do you have Firefox and its Web Developer and Firebug extensions yet? Those are especially valuable for unraveling a convoluted mass like the TM structure. Reading the .main_t .row1 .col2 .etc {} style rules in the stylesheet by eye can be mind-numbing.