If you have the
Traders and Builders expansion, then everyone also gets one Builder meeple.
A builder can be placed (in place of a regular meeple) in a city or on a road that you own. This means that you cannot place a builder as the first meeple in a city or on a road, you have to "own" it first. Like a pig, you cannot place a builder in a city if the city contains meeples for another player as well as your own.
In play, if you play a tile that extends the city or road that the builder is on, you get to pull another tile and play again (although if you build on the same city/road as the builder on your extra turn, you don't get to go again).