To sell or buy Danone shares, you can use the services of an online broker or trading platform. Start by opening a trading account with a reputable online broker. Next, search for Danone's ticker symbol, which is 'BN' on Euronext Paris. Use your broker's trading interface to place an order to buy or sell Danone shares, specifying the number of shares you wish to buy or sell and the price at which you are prepared to execute the transaction. Once your order has been placed, it will be executed on the stock market.