Complex sentence: When invoked without any arguments, ls lists the files in the current working directory-but if another directory is specified, then ls will list the files there, and in fact the user may specify any list of files and directories to be be listed.
Split into simpler sentences: When invoked without any arguments, ls lists the files in the current working directory, but if another directory is specified, then ls will list the files there. In fact, the user may specify any list of files and directoriesto be be listed.