I illustrate , wat i understood.
here X is randome variable having posssible value 1,2,3 and probability density function concept is used .
pr (xi=0) getting of x1 and x0=1/2 not getting for i=1,2,3 , xor concept i know welll . pr[y=0|x3=0] it is conditional proability . Now find out what is mistake in my thinking.