Most people have dandelion plants in their lawns. Some would even go so far as to say their lawns are "ruined" by dandelion.
Actually, this pretty plant is not a weed (though it grows and spreads so easily it acts like one). It's a longstanding common herb that is full of vitamins A & C and iron.
The leaves are sweetest before the flower forms. After that they taste bitter, so are best cooked, which removes some of the bitterness.
First a word of caution - don't pick dandelion in parks or by roadsides, they are likely to have been sprayed with weedkiller, which of course is poisonous.
Instead pick them from your own lawn (making sure you haven't put weedkiller on your lawn).
Wash the leaves thoroughly and then cook them in any recipe that requires greens. They make a good substitute for spinach.
The roots are also edible. When you dig out the roots, wash them thoroughly and then peel off the skin (the skin is bitter). After that, cook them the way you would cook carrots.