When writing chemical or mathematical equations in Microsoft Word it is often easiest to use the equation editor.
This editor allows you better formatting than entering a formula with the standard tools. It’s also supplied with most copies of Microsoft Office, which you will probably find installed on institution/corporate computer facilities.
I have prepared this using Microsoft Office 2007. If your Office looks different, you should be able to find Equation Editor in “Insert > Object > Microsoft Equation 3.0”. If you can’t find it at all then you will need to install it from your Microsoft Office CD (this site shows you how to install).
If you don’t have MS Office then you could use a free editor such as this LateX Equation Editor which will render your equations as images which you can then copy into your work. They have a working trial at the top of the page, click the center image to load it.
The equation editor contains quite a few pre-set equations which you can enter automatically and gives you access to all the symbols you will need.
Quite simply, find out more through practice! There are more in depth guides available on this tool, including this one for older versions of Office. A simple google search will reveal more information.