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.
Click on the the template. At the bottom right of the dialogue you'll see two options: 'Document' and 'Template'. If you want to use the letterhead to send as a document or letter, choose 'Document.' If you want to edit the template, choose 'Template.' When you choose 'Document,' it gets saved as an MS Word document.