Originally Posted by Nazish Hina

You don't require the background. It is one of the most interesting subjects you'll study and you will enjoy it too. It is not confusing at all except one chapter about the function of brain which took me slightly more time.

Use a book which is interesting and has illustrations and experiments to help you understand better.

Other than that there is a series of Psychology lectures by Yale university which coincides with the CSS syllabus. There are also a "Crash Course" in Psychology by Hank Green.
The book I used was FPSC recommended Atkinson and Hilgard's Introduction to psychology, Other than that I used Introduction to psychology by J.W.kalat.
I hope this helps, have a nice prep