Exam

Assuming that you have never studied psychology before in school or otherwise, I would suggest that first, you go through NCERT books of class 11th and 12th psychology.
Once you are clear about the concepts there.
You can move on to a graduation level book of psychology. A book called "Intro. to psychology" by Robert Baron is a must. It covers all most all basics and is a recommended reading in most undergraduate courses of psychology.
In addition to that, there is a wonderful online course on psychology by Yale University conducted by professor Paul Bloom. You can find it on YouTube. These lectures are easy to understand and professor Bloom doesn't bore you.
There are, of course, other lecture series such as one by Berkeley, and others, you can watch them but I feel, Bloom's series is sufficient and easy to grasp at least for entrances purposes.
Entrances to MA Psychology and MA Applied Psychology are usually conducted around May-July, assuming that you are aiming for these, I would recommend the above "three" only.
Written entrances in DU are of MCQ type, so if you "really" clear about basics, you can clear the written exam.