The fact is that the buying and the selling of the stocks that you wish to do through your investment cannot be entirely carried out by you; this is the reason why you will need a professional stock broker who would be able to sell or buy stocks whenever you give the order to do so.

How it works is very simple, the stock brokers manage an account in your name with their company or firm. The account works in a similar fashion as the accounts in banks do. The only difference is that besides safely keeping your money the account in your name will also contain the stocks and shares that are in your name.

So whenever you make money by selling some shares or through some investing that you have done that amount gets credited directly into this account which is in your name. Similarly if you need to invest your money somewhere or buy bonds etc., the money for that transaction is taken from this account; all of which is managed by your stock broker under your order and wishes. There are full service and discount stock brokers who have varying features.