For example, if I am building a huge golf course, and I am talking to a friend, at a restaurant, and I am showing him the map of my golf course by gesturing in the air with my hands (there is no real map). Kinda like how grand my golf course will be, and here will be the swimming pool, and here the bar, etc etc.
Use gestures, especially dramatic ones, instead of speaking or to emphasize one's words.
‘they were shouting and gesticulating frantically at drivers who did not slow down’
I showed him the map gesticulating my grand vision for the course, swimming pool here, bar over there...