When you peddle something, you go out and try to sell it. It's cute when a little kid peddles his homemade birthday cards around the neighborhood, but if an adult did that it might be annoying.
The classic image of someone who peddles is an old-fashioned "peddler" or "tinker" traveling from village to village selling goods. The verb peddle, in fact, came from the word "peddler," whose origin is a mystery. Any time you sell something by going from place to place, like selling Girl Scout cookies to all your neighbors, you peddle. Don't confuse peddle with homophones pedal, the bike part, or petal, the flower part.
