They must use 'plc' after the company name. Again this warns people that the owners of the company have limited liability.
Their shares can be bought and sold on the stock exchange.
There can be a separation of ownership and control. This occurs because the owners (shareholders) are not involved in the day-to-day running of the company, which is left to the managers. The objectives of the owners may differ from those of the managers; owners will want the business to earn as much profit as possible whereas the managers may simply want an easy life.
The shareholders are allowed to sell their shares to anyone they want. They could even decide to sell their shares to another company, which might lead to a takeover.