"To honk the horn" means to press the button or lever in a vehicle that produces a loud sound to alert others or get their attention.
Sentences with «to honk the horn»
Drivers passing by honked their horns in support. (sun-sentinel.com)
I got pointed the finger several times and people honked the horn at me and yelled from the window It's hard to be a nonbeliever in America... I live in New Jersey BTW. (religion.blogs.cnn.com)
After I made the realization, I felt offended every time someone honked their horn when they drove past me. (brittanymthiessen.com)