I have just spent some time trying to figure out some of the finer details of this data merge process in PM and have learned a few things.
1. The data source can be created in any program that allows you to save it in 'comma separated values' format (*.csv) - the best is Excel (or Word tables).
2. The columns of data in this source should have headings e.g. 'firstname', 'lastname', 'address1' etc.
3. When you set up the fields in PM, you must do it within a text frame (the symbol on the toolbar is a rectangle with a cross through it). So first step is to draw a frame the size of the completed card/certificate or whatever.
If there is to be more than one record per page, then draw up a dummy of the layout showing how many records are to appear on each page, and check the measurements. If there is to be more than one record ACROSS the page, then take note of the 'column gutter' i.e. space between each card. If there is to be more than one record DOWN the page, take note of the 'row gutter'.
4. Back to the actual merge layout. Set up the layout and format of the fields ONCE only - even if you want more than one record per page. If you repeat the record layout, you will get repeating instances of the one set of data.
5. Using the text tool, insert the fields in the appropriate places within the text frame, clicking on the list in the Merge palette to select the fields.
5. When you are ready to do the merge, click on the flyout arrow on the Merge palette and choose 'merge records'. Under the layout options, choose 'manual layout' from the drop down menu. Once this is selected, the column gutter and row gutter become enabled.
6. Enter the column and row gutter measurements. If there is only one record ACROSS the page, you can leave the 'col gutter' blank.
7. You can check the box to remove blank lines (e.g. some addresses may have more or less lines than others) and uncheck 'embed images' as it makes the process much slower.
8. Click OK and let PM do it's magic.
Note that the process results in the production of a NEW document and leaves the original 'master' unchanged. So if it doesn't work correctly, you can close the new document without saving and it will take you back to the original.
You can also insert images into each record e.g. a logo, but that's another tutorial!