The easiest ways are either to get the train from London Paddington (direct service with First Great Western) or take National Express coach 444 from London Victoria Coach Station.
The best option is to get a First Great Western service from London Paddington. It's a direct journey and typically takes around two hours and a quarter.
The City of London is the name of an area of London, where the stock markets are etc. London is a city, but the actual "City of London" is an area between East and Central London. The City of London...