Botanical Name: Sambucus nigra
Energetics: Cooling, moistening
Major Properties: Antipyretic (reduce fever), diaphoretic
Examples of Uses: Reduce fever by sweating it out
Parts Used: Flowers fresh or dried
Honey - I enjoy elderflower steeped in honey - lovely taste and easy way to use through the winter
Dried for tea - maybe add some lemon balm and rosehips for a lovely tea with great immune boost.
I use elderflower largely to reduce fever if it is getting too high or achy. Otherwise, a fever is a good thing for burning off pathogens.
I combine elderflower, peppermint, and yarrow into a tincture for fever. Might cause the fever to rise a bit as it gets pushed to the surface, where the diaphoretic action will also open pores to let it out. That's a very simple answer...
This brief overview merely highlights my observations. There is, of course, a great deal of information that you can find on the Internet or in books. Or better yet - get together with other herbalists and share your experiences!
Please add your own experiences so that together we can create a more comprehensive overview.
As always, if you have a chronic ailment that is not resolving itself or an acute issue, seek the attention of your physician.