Hyy Rajasree
If you want to persue psychology in your Graduation that great it's a fabulous subject and if you have not studied it before don't worry. You will not face any major difficulty once you start studying it everyday.
I have studied psychology in 12 and now going to complete my graduation in psychology.  In graduation they will not be teaching any rocket science in these subjects cause 1 semester always includes Introduction that is totally based upon your 11th class content and there is no previous knowledge required to top this subject.
I will recommend you some books that will definitely help you In psychology
Introduction to psychology by Robert A.Baron . Which is easily available on internet as soft copy as well as to purchase.
All the very best for the future :)
Hope this helps you
For more queries and information please ask in comments section