These berries should not be eaten raw, especially unripe berries from lower than 2m away from the ground, as the whole plant (including the berries) contain enough cyanide and toxins to make you quite sick.
That said, Both flowers and berries can be made into elderberry wine. The alcoholic drink sambuca is made by infusing elderberries and anise into alcohol.
The mild cyanide toxicity is destroyed by cooking. The berries can also be made into jam.
The flowers may be used to make an herbal tea, which is believed as a remedy for colds and fever. The flowers can also be used to make a mildly alcoholic, sparkling elderflower 'champagne'. My Aunt (in the Cotswolds) is an expert at this!