The key is to define a small number of summary fields in your donations table and then set up one or more summary report layouts based on the donations table with fields included from the donors table as needed to supply donor information.
You can perform finds and sorts to manipulate the found set to get quite a few different reports.
Here's a tutorial on summary reports that you may find useful: Creating Filemaker Pro summary reports--Tutorial
If you have any question about that tutorial, please use "Post A Answer" to post them here, not in that thread as threads of that age no longer automatically appear in the Recent Items list if you post a comment to them (and thus, I am unlikely to notice any comments posted to it).
Many thanks Phil, I was thinking that way and it is great to have one's wonderings confirmed.