Builders know what to do because they have special plans made by engineers. Think of it like a treasure map! Just like when you follow a map to find treasure, builders follow the plans to build things like houses or parks.
Engineers are like the smart inventors who design everything. They draw pictures and write instructions on paper to show the builders how to do their job. The plans tell the builders what materials to use, how tall to build, and even how to make things safe.
So, when the builders have their special plans from the engineers, they know exactly what steps to take, just like following a recipe to make a yummy cake!