Hi Rajesh,
Firstly ABAP is a good career option.There is no prerequisite to learn SAP ABAP.But there are less opportunities for freshers.
Before joining any company you can go for some ABAP training.If not possible,then you can atleast learn from **************** and other websites.
For real time experience you should know about the process within different modules(MM,SD etc).
Secondly you should know about basic transactions and their use.
All the best in advance.
Regards ,
Neha Ghazi