Dandelions are incredibly abundant, which makes them a forager's dream. Even better is that almost the entire plant can be used - leaves, flowers and roots. The young leaves make a great addition to salads, bring a sharp, bitter taste to the mix.
Alternatively, they can be sautéed in oil and garlic, like other leafy greens, and enjoyed as a side dish. The roots can be used for making a caffeine-free coffee-like drink, and the yellow heads can be fried, baked into a bread or scones, or made into wine.
In fact, the only parts that can't be consumed are the puffy seed heads.
As dandelions are weeds, the main caution that must be taken while foraging is to avoid areas that may had had weedkiller sprayed on them, such as public grassy verges, or where dogs may have peed on them.
Generally, it's discouraged to uproot a plant for the sake of foraging, because this damages the plant population. However, as dandelions are so abundant, you could use them roots of these if you take them sparingly from land you have permission to forage from.
Try to avoid taking the flowers in early spring, when they are a key food source for bees.