Parent #1 has the alleles of IA and i
Parent #2 has the alleles of IB and i
A punnet squares is a simple diagram that illustrates the possible genotypes of the offspring of these two people.
Parent #1 is across the top and Parent #2 is along the side
IA i
IB AB IBi
i IAi ii
For IA or IB will be dominant to i. So for phenotype purposes their offspring have a 25% chande of being AB, 25% chance of B, 25% chance of A and a 25% change of type O (ii)