I would like to add some specifications here.If I own Bitcoin, do I automatically own Bitcoin Cash too?
"If I own Bitcoin, do I automatically own Bitcoin Cash too?" - as well as I know it depends on where you stored your btc before the first of August. If it was on the exchanger or some online wallet, you probably won't get your bcc.
"Why was a fork necessary to create Bitcoin Cash?" - I think it wasn't. Something had to be done and with btc is was done indeed. Bitcoin has a segregated witness technology now, so it has solved the problems with transactions. Bitcoin cash was supposed to be a back up plan but, as too many people got interested, it was released anyway.