for this you would use a punnet square (ill try my best to show it while typing)
heterozygous means different, so (with blood type) with heterozygous A you will see AO (this will be blood type A)
A O
B AB BO
O AO OO
you then have the types in the squares:
AB (type AB blood)
BO (type B blood)
AO (type A blood)
OO (type O blood)
