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, comes 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.