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Both your puppy and your cat need a room in which they can adjust. You do not want to force a meeting right away. Give your pets separate care and attention for the first day or two. You should usually confine the new pet initially, meaning you should keep your puppy in a separate room before letting her roam around the house. Make sure the room is stocked with adequate food, water, and toys. Make sure to spend plenty of time with your new puppy as she adjusts to your home. You should switch out which animal is confined. This will give them each a chance to explore the home. They can also get used to one another's smells, and become increasingly comfortable with the fact a new animal is present. Rotate the animals every few hours. It's important the puppy has a chance to leave the room and explore a little, but you should not allow her free-range of the house yet, as this may interfere with potty training. Expand the area in which the puppy is confined to two or three rooms and watch her closely to watch for signs of toileting. When the animals are not confined, they may interact through the door. Your dog may, for example, sniff or paw at the door. For the most part, this is safe; however, if your puppy is excessively pawing at the door, correct the behavior. This can cause stress for your cat, leading to a messy introduction. It's very important the dog and the cat get accustomed to one another's scent. You can swap small bits of bedding, like pillows or blankets. You can also exchange toys. Try rubbing a towel on one animal and putting the towel under the other animal's food dish. You should never leave your pets unsupervised before you've made many successful face-to-face introductions. Make sure both the dog and cat are securely confined to separate areas when no one is home. You may wish tocrate train your puppy and keep her safely confined while you are out, allowing the cat free range (as he is presumably already comfortable in the house) If you secure the cat in a room while you're gone, make sure he has access to a litter box.
Set up a space to confine your cat or dog. Alternate which animal is confined. Exchange scents. Keep the animals confined while no one is home.