stocks are issued by companies which have a need for capital. stocks do noth have definite term or maturity. they will exists as long as the company exist and they have a positive value.
as the value of the company changes, the share price of the company will also change.
when individual or investors are purchasing the stock they become owers within the company. there level of ownership will depend on the number of shares they purchased . as owners they have the right to participate to meetings organised by the companies.