My puppy loses focus when he sees people/dogs/cats when we walk outside?

So I just adopted a 5 month old dachschun mix and he is sweet and adorable. We take him to his grammy's house to have a playdate with another dog every weekend. My problem with him is everytime we are outside and he sees other people/dogs/cats he won't stop whining and sometimes I let him meet them but he is just nonstop. His focus is just on that person/animal and he won't listen to me. What should I do? How do I train him to focus on what were doing (walking/playing fetch/etc)?