A blacksmith is someone who makes things out of metal, particularly iron, for a living. Blacksmiths use tools like a forge, hammer and anvil. Blacksmiths make items like tools, weapons and furniture from iron.
Someone who makes horseshoes is called a farrier, not a blacksmith.
A myth is a story that doesn't have a basis in reality, but that many people think is true. A good example of a myth is that you can catch a cold by going outside in cold weather.
Pith is the spongy material found inside plant stems. When you are talking about citrus fruit, pith is the bitter white layer surrounding the sweet flesh of the fruit.