A family of Microsoft word processing software products for creating web, email, and print documents.
Suzanne has explained how to display the Insert Field dialog box and use it to insert a field.
If you are saying that you want to create a Building Block which includes a field, you can do that the same way you create any Building Block. Select the content you want to store and then press Alt+F3. Finally, specify a saving location and a name for the entry.