Not quite.
"Duplicate" will create a copy of the file or folder instantly, in the same location as the original file. The new file will be named with the word "copy" as a suffix. If you continue to create duplicates, they'll be called "copy 2", "copy 3" and so on.
"Copy" will effectively place the file or folder in a kind of clipboard / holding pattern, and you can then browse in the Finder to another location and use Paste to save a copy to the new location. It will be given the same name as the original (no "copy" suffix) unless a file of that name already exists, in which case you'll be prompted to overwrite it. If you do a copy/paste operation in the same folder as the original, it'll have the same effect as Duplicate.
Matt