You also have several templates to choose from with Open Office software, but Microsoft Word provides a wider selection. However, if you do find a template that seems good enough and you'd like to customize it, go to Wordlabel.com to download the file. To open it, right click Open With and then select the software. You can then modify it however you want.
Why create one? _ "Re_inventing the wheel", is no fun. If you work for a single organisation it's likely that your templates could last a long, long time with no need to go back to the design board every time you are asked to create a new manual or user guide. When you work for yourself it's a great way to show clients that you have the skills they are looking for without breaking any confidentiality clauses with your existing clients, and with just a little bit of luck they'll adopt your method of working so you can continue to recycle your past efforts too.