Sounds like you are talking about a mail merge.
Click on HELP (in word) and search for mail merge. (That's where the below came from....)
About mail merge for form letters and mass mailings
Use the Mail Merge Wizard to create form letters, mailing labels, envelopes, directories, and mass e-mail and fax distributions. To complete the basic process, you:
Open or create a main document.
Open or create a data source with individual recipient information.
Add or customize merge fields in the main document.
Merge data from the data source into the main document to create a new, merged document.