I want to use XeTeX so that I can use a particular font, but I'm not quite sure about the documentation/commands in specifying this font in XeTeX. Can anyone point me to a good how-to tutorial on XeTeX?
If you're planning on using XeLaTeX, and already know LaTeX, the fontspec documentation contains just about everything you need to know additionally.
As for good reference, there is the XeTeX manual itself (from CTAN, but see
texdoc xetex) and this draft textbook: The XETEX Companion. TEX meets OpenType and Unicode, by Michel Goossens. The XeTeX webpage also includes some useful link.
Handling fonts with XeTeX has already been extensively discussed on this site; I would suggest to look for related tags.