shares is issued by a company to collect the funds from 
people.If the share fund is not enough to the company they 
issue the debentures.In shares the company will give some 
percentange of the benefit to his shareholders,for the 
depentures the company has to pay a certain percentage of 
amount to his share holder.

Shares are issued by public limited companies for mobilizing
their capital.for which companies are paying dividend in
annualy or 6 months once.

Debentures are issued by public limited companies for
mobilizing additional capital and for which companies are
paying certain percentage of interest in annually.

Difference between shares & Debenture is :

Share holders eligible for voting ,bonus shares,Right issue
of shares and they are liable upto their shareholding to
companies liabilities in case of liquidation of the company.

where as debenture holders are investors like bank
depositors and they are eligible for interest and preference
 in getting back their investments in case of insolvency of
the company.