OS X comes with a number of fonts, and if you install third-party software such as Microsoft Office or Adobe's Creative Suite, your system may be inundated with them. This may not be that big of an issue, but if you want to see what a font looks like before picking one to use, having to slog through a large list to do so is impractical.
Fortunately, there are several options in OS X for previewing fonts that can help streamline the process, some of which may be more available or useful than others:
In most word processing and design applications you can access fonts from a built-in font menu, but sometimes, either because of a program limitation or by design, these menus only show you the font name and not a preview of its typeface. For those programs that do support the function, you can preview the typeface by toggling a setting in the program. For example, the Font menu in TextEdit does not support displaying typefaces, whereas in Pages you can hold the Option key while opening the Font menu to toggle font previews, or set this in the program's preferences.
In addition to the Font menu, many programs in OS X make Apple's Font panel available as a means for customizing typefaces. This can sometimes be accessed by pressing Command-T, but should otherwise be available somewhere in menus like Edit, Font, or Format, depending on the program being used.
The Font panel offers access to font collections and families, and allows you to select and preview them to see their various typefaces. This is still not the best solution for previewing fonts, but it may be more convenient than selecting your text in a document and then setting the font one at a time.
In addition to the font panel is the Font Book utility, which as Apple's built-in font management utility, allows you to browse your fonts and see previews, but as with the font panel, it does not show typefaces in a list.
A final option for previewing fonts is to make use of stacks in the OS X Dock. Stacks is where you can drag a folder to the Dock and then click it to view a listing of its contents in a grid, list, or a "fan" view instead of opening it in a Finder window. If you do this for the font folders in the system, then you can take advantage of this previewing feature to get a glimpse at the font files' typefaces. Simply locate and drag the following two folders to the Dock, and then right-click the folders in the Dock and set them to Grid view.
In the Font folder stack, the typefaces you see will simply be shown as little boxes that say "Ag." Scroll through the list, hover your mouse over a font, and press the space bar; you will be given a QuickLook preview of the font's standard alphanumeric characters. You can use this to quickly go through your fonts and pick the one you want to use. Just be sure not to open the font from this menu; doing so will launch the Font Book program.
The font folders in OS X are available in the following locations:
Macintosh HD/Library/Fonts (this is the primary font location)
OS X comes with a number of fonts itself, and if you install third-party software such as Microsoft Office or Adobe's Creative Suite, then your system may be inundated with fonts. This may not be that big of an issue, but if you are interested in searching for a font by its style, having to slog through a large font list can be a bit of a burden.