Continuing your metaphor, PaperDolls have Accessories. This is a many-to-many relationship in that one accessory can be added to more than one doll and a doll can have many accessories. So, you need a table that stores the combinations. This is called a Join table. All you need in this table are DollID and AccessoryID. Your report would be created from the context of the join table.
Expanding on that, you can place fields from the related tables on your report layout that is based on the join table. You can place these fields in headers, sub summary, and other parts if you need to show the data only once for all or a group of records.
In a one to many relationship such as invoices to line items, you can create your report based on the line items table and use the above method to show data from the Invoice table in a header or subsummary part.
If you want to see how that works in a summary report, see this tutorial: Creating Filemaker Pro summary reports--Tutorial
Thank you both for these answers. bcooney has pointed me to right direction and now I need to do some studying, but it might take some time as I'm doing this on my spare time which at the moment is a rare phenomenon.
Most likely I'll get back here when I'm struggling to get things to work.
Thanks so far!