Fonts such as Arial come with mathematical symbols that you can insert as individual Unicode characters using Insert...Symbol menu item.
What kind of formulas does your user need to create? The more elaborate they get, the more likely you will be wanting to invest in a special math font such as Lucida math (134 roman and greek characters plus numbers) or Lucida math extension (133 mathematical operators)
http://www.linotype.com/57803/lucidamath-family.html You can see the character sets by hitting the link for "More details..." followed by the one for "Encoding map"
