In short:
A = torch.tensor([1,0])
B = torch.tensor( [ [1,2,3] , [4, 5, 6] ] )
A = A.unsqueeze(1)
C = A * B
print(C)

Which gives as output:
C = tensor([[1, 2, 3],
        [0, 0, 0]])

You can use broadcasting 55 for these type of problems.