The elderberries (Sambucus nigra) are in full flower now. If you happen to be a splitter instead of a lumper, then I suppose it is fair to say that both S. nigra and S. canadensis are in bloom.
The flowers give rise to the little black-purple berries that are made into jelly, and are used as a cold medicine. The flowers can themselves be used as a flavoring, a food, and possibly a medicine. One approach is to make a crude variant of elderflower cordial. Pack a quart mason jar full of the flowers, and cover them with vodka for a day or two. After that, strain out the flowers and keep the vodka. Keep it stored out of direct light. Most vodka will be around 80 proof (about 40%) and can be cut (possibly with sugar water if you want it sweet) 50/50 for a final alcohol content of around 20%.
I’ve read that you can batter and fry the flower bunches, but I’ve never tried doing that. Let me know if you do.
You can steep the elderflowers in a light syrup as well. This omits the vodka, and syrup recipes are included in any basic cooking book. Syrups will pull some moisture from the flowers, and the flowers do not provide any prevention against fermentation or spoilage. So unless you us a syrup with sufficient sugar concentration to prevent spoilage, you’ll need to keep it refrigerated, frozen, or can it.