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.
On the top of MS Word you'll find the menu bar. Click on 'View' and then 'Header and Footer.' What appears is a dotted box already with a cursor inside. A floating menu bar also appears.