Solving Hardy Weinberg problems?

Question

I really fail to understand Hardy-Weinberg equilibrium and can't find an easy enough source of information. Can you help me to understand Hardy-Weinberg equilibrium? My goal is to be able to solve the following kind of problem > In a population with two alleles for a certain locus, B and b, the allele frequency of B is 0.7. What is the frequency of heterozygotes if the population is in Hardy-Weinberg equilibrium?

Answer 1

B = 0.7 and b = 0.3

Heterozygotes would be 2pq where B is your p and q is your b, therefore 2pq=2*.7*.3=0.42