Question

What are the purpose of gargoyles what do they do ?

Answer 1

They were like rain gutters or spouts

Answer 2

Architects started to include gargoyles in churches in times when most people couldn't write or read. Their function was to "say" that such monsters/ghosts/spirits/forces are dangerous outside and the only place one can be safe is the church itself. Eventually this form of communication worked as thanks to the gargoyles there were more and more believers among christians.