Usage

ln source_file hardlink
ln -s source_file symlink

Difference between symbolic and hard links

Hard link can only be created for a file.
Symbolic link can link to a directory (folder).
If you remove the hard link or the symlink itself, the source file will stay intact.
Removing the source file that your hard link points to does not remove the hardlink itself; the hardlink still provides the content of the underlying file.
Removing the source file does not remove the attached symbolic link or symlink, but without the source file, the symlink is useless (the same concept like Windows shortcut).