Edible flowers bring colour, fragrance and sometimes a surprising flavour to the plate. I often use dried ones, such as calendula, rose and cornflower, which in winter add a touch of colour to risottos, grains, soups and salads.
Many others are used fresh: deep blue borage flowers, rosemary, lavender, mallow, nasturtium and courgette flowers. Some are delicate, others peppery, others fragrant like honey.
One important rule: only use flowers you are sure about, grown to be eaten or picked in clean areas, away from roads and never treated. If you want to know more, I wrote an article about it, "Eating flowers".