How do I copy a file that is on the server

I want to copy a file like the cp command in unix. I may not want to move a file I may want to make a copy of it in another directory. Or I may jsut not want to start from sctratch and make a copy of a file that is similar. This should be a very common operation, and is part of most other ftp programs. But I can't seem to copy a file here without moving it from the server to my machine first, and that is just silly.