[lozf]

The source is the only thing to worry about. Without a trailing slash it makes a copy of the directory, and fills it. With a trailing slash, it copies just the *Contents* of the directory.

    rsync -avP foo bar   # puts foo inside bar so bar/foo/* 
    rsync -avP foo/ bar  # puts the the contents of foo, in bar (without making foo)

I like to add the v & P flags for verbosity & progress.