what does "ls -a" do code example

Example 1: ls -a

ls command list computer files in a directory in Unix OS with next structure:
ls [OPTION]... [FILE]...
Examples:
ls -l #display all files in current directory with  (-l) long format.
ls -a /directory #display all hidden files in given directory that start with .

Example 2: ls -l

0 success
1 minor problems  (e.g., failure to access a file or directory not
  specified as a command line argument.  This happens when listing a
  directory in which entries are actively being removed or renamed.)
2 serious trouble (e.g., memory exhausted, invalid option, failure
  to access a file or directory specified as a command line argument
  or a directory loop)