If you'll only be using manually-entered data in OnMerge you can ignore this section.

You'll need to make sure that Word is connected to a source of merge data such as a spreadsheet or database to use OnMerge with Mail Merge:

• Make sure to open the datasource before running OnMerge since otherwise OnMerge won't be able to "see" which data fields are available.
• For data from Excel, Access, SQL and many others, use Word's built-in Select Recipients button in the Mailings toolbar.
• Comma Separated Values (CSV) files and Tab Separated Values (TSV) files need special treatment, even if they were made by Excel. Those files typically end with .CSV, .TXT, .TAB. Use OnMerge's special CSV Loader button in the Mailings toolbar instead.

NB Word assumes the first row of CSV files contains column names. That's usually so, but some CSVs start right in with actual data in the first row. That will make it seem like the first row of data is missing, and your data fields will seem to have strange names. Uncheck First row of CSV is column header names in the CSV Loader dialog to solve the problem. Fields will be named F1, F2, etc.

NB The CSV Loader was added to OnMerge in version 3.21. Please upgrade if you have an earlier version and need this feature.