Click on 'File' at the menu bar and then click on 'Save As.' Name the document. Then, just below the file name is the dialogue, 'Save as type:'. Choose 'Document Template (*.dot).' You'll notice the directory at the top of the dialogue box changes to 'Templates.' Click 'Save' and you're done.
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.