Your first step in preparing a mail merge is to create your main document—the document that contains any boilerplate text that should appear in all your merged documents, as well as instructions about which kinds of information should be merged into them (mail merge fields). You can create one of four kinds of main documents:
When you create a form letter, Word creates a new letter for each set of merge data.
When you create envelopes, Word creates a new envelope for each set of merge data.
When you create labels, Word creates new labels for each set of merge data.
When you create a catalog, Word creates only one new document that contains all the merged data. Word repeats any standard text you add to the catalog main document ...