A film is the result of many creative processes directed towards a single goal - tell the Story. And to tell the story through a film what's indispensable are the tools such as cinematography, writing, editing, music, sound design, production design, or costumes etc. and off course the actors.
While every single aspect is looked after by a head of the particular department, 'Director' is the one who coordinates all these creative activities involved towards the making of a film. In other words, director is the head of the entire creative team consisting of cinematographer, editor, sound designer, music director, action director, writers, actors etc.