Invitation is a way to ask some one to go to an event or a place or to do something.The function of invitation is to ask some one to go to a place or to do something.We usually use the “invitation” in our daily life, for example if we want to hold an event like a birthday party . We use the invitaion and if we want some one to do something , like if we want our friend to help us.We use the invitation too.