Really need ! how do i memorise a paragraph for

The best way to memorize a paragraph fast is to keep re reading it, or writing it down over and over again. 

It isn't easy.  You need to read it and understand it.
Then, I suggest you write it down, trying to rephrase it a bit, to make it shorter.  Then do that again.  If you can do that, you end up using only a few words to remind you about the whole paragraph.

Good luck!