Most Emacs commands that operate on a file require you to specify the file name.
Completion is available, to make it easier to specify long file names.
See Completion . For most operations, there is a default file name which is used if you type just RET to enter an empty argument. Each buffer has a default directory, normally the same as the directory of the file visited in that buffer. When you enter a file name without a directory, the default directory is used. If you specify a directory in a relative fashion, with a name that does not start with a slash, it is interpreted with respect to the default directory.