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.
When you want to call up that template, here's what you do. In your MS Word, click on 'File' (take note that you don't click on the File icon, but the word, 'File.' When you do so, a dialogue box appears from where you can choose the template you just created.