well first, i'd like to tell you that it's not replicate it's replica. copy means reproduction whereas replica means the exact copy of picture or a real copy made by original artist. now, replicate means folded back on itself. i think it'd help.

They mean the same, but copy is used more often.

There is no real difference. But we use the word copy more because it sounds more simple and informal. When speaking of documentation at least we always use copy. Examples: "I am going to make a copy of that form" "Do I need a copy of this with me?" But the word copy can also be used in many other cases where one could use replicate. Examples "We are going to copy/replicate the process." "You must copy/replicate this design."