"The actors are coming out from behind the curtain, on which there is a big butterfly."
Translation:A színészek a mögül a függöny mögül jönnek ki, amin egy nagy pillangó van.
Let me demonstrate with a simple example. It is too difficult to explain but this should do:
I did not get the position (that) I was promised - "amely"/"amelyik".
I did not get the position, which is a shame - "ami"
"Ami" refers to the whole previous clause.
There is some acceptable overlap between "amely" and "ami", which is perfectly fine, in some situations. But there is some serious misuse going on these days when just about anyone can be a writer.