n is the required sample size
N is the population size
p and q are the population proportions. (If you don't know what these, are set them each to 0.5.
z is the value that specifies the level of confidence you want in your confidence interval when you analyze your data. Typical levels of confidence for surveys are 95%, in which case z is set to 1.96.
E sets the accuracy of your sample proportions. If you want to know what proportion of individuals are in favour of some policy, with an accuracy of plus or minus 3%, then E is set to 0.03.