I eat them.
If they're young leaves, new growth, then they're just like a salad green that's on the bitter side. Very nutritious too. I'm waiting patiently for the first ones to pop up. Should be a couple of weeks here. I usually just mix them in with other salad greens.
When the leaves grow bigger they can get quite bitter and tough. I usually only eat the young leaves but have used older ones cooked in soups. Like you would spinach or chard.
You can also just sautee young or older leaves(depending on your like of bitter) in butter.
All parts of the plant are edible though I find the stems quite bitter. Probably would be okay in some sort of soup or stew though. The flowers can be made into wine though I haven't done that. I have made jelly out of them but that uses tons of sugar. You can also just use the petals to liven up salads with some color. The roots can be dug up and dried and brewed like a tea.
Other 'weeds' I regularly eat are plantains and chickweed. Chickweed is delicious just raw. Plantain is good in soups and sauteed. I also eat nettles, burdock roots, chicory and red clover flowers. Clover flowers are like a delicacy to me. If you get them at the peak of flowering they're crunchy with slight sweetness. You can also dry them and use them for a tea.