Hi,
Add fields to a form letter or other mail-merge document
In step 4 of the Mail Merge task pane, you can add addresses, greetings, and other personalized merge fields.
1. In the main document, click where you want to insert the field.
2. Insert any of the following:
- Address block with name, address, and other information
- Other fields of information
3. Repeat steps 1 and 2 for all the fields you want to insert.
Notes
- You can't type merge field characters («« »») manually or use the Symbol command on the Insert menu. You must use the Mail Merge task pane.
- If the merge fields appear inside braces, such as { MERGEFIELD City }, then Microsoft Word is displaying field codes instead of field results. This doesn't affect the merge, but if you want to display the results instead, right-click the field code, and then click Toggle Field Codes on the shortcut menu.
Reference - http://office.microsoft.com/en-us/word-help/add-fields-to-a-form-letter-or-other-mail-merge-document-HP005187661.aspx