See:

• Create a Form Using Word Content Controls by Greg Maxey
• Making Forms with Microsoft Word

Do not combine both Content Controls and legacy form fields in the same document.

A key to keeping other text from moving, if that is truly what you want, is to place your Content Controls in a table. There need be no borders displayed or printed on these tables.

• 4. Use Tables and Tabs to Arrange Text in Microsoft Word
• Tables