Put your new puppy in a cage and allow your cat to approach/explore the newcomer. As your cat is probably used to being the only pet around the house, it could also be jealous. Always supervise their interaction to avoid unnecessary injuries.
Do not thrust the cat or puppy at the other. Reassure and show the cat that you love him too – he could be jealous and hostile because you might be ignoring him because of the cute new puppy!
Please note that some cats may never accept another newcomer. Hence, assess the personality of your existing pet carefully before deciding to bring home another animal.