It is not uncommon for people to bring home a second dog, and often do not know how to help facilitate a positive introduction. This video does an excellent of of demonstrating how to do that in a neutral place. It also talks about acclimating a newly adopted pet upon your first arrival home.

To Have A Better-Behaved Dog, Consider What Happens Between Your Training Sessions
Every waking moment of every day and every interaction your dog has with you and the environment is teaching your dog what works, what matters, and what associations to have.