Whether you've gotten a new pet, or undergone a recent move, your cat will probably need some time to adjust to his new surroundings. It may be a good idea to introduce them in a neutral area outside your home, so that they can become familiarized without either pet feeling intruded upon.  If bringing a new pet into your home, keep the new pet separate from your current cat(s), and provide the new pet separate food, water, and a litter box. Allow the pets to socialize in your home gradually, over a period of several days to several weeks.  Introduce them first by scent by letting the cats each sleep on a piece of your old clothing that has your scent on it as an intermediary. The next night, swap the clothing over so the cats get a whiff of each other's scent. This "Scent handshake" can smooth over the introduction as they learn about one another. Keep an aggressive cat in his carrier during introductions, if he has displayed hissing and other aggressive behavior toward the new pet.  Humans often cannot detect cat scent marks.  Use a handheld blacklight, available at any pet store, to look for cat urine stains on walls and furniture. When cats fight, they often receive wounds that are not obviously visible.  Carefully examine the animal by approaching the cat slowly, and gently running your hands over its body looking for tender spots.  Your cat will let you know if you've found one, so don't poke or prod. If you find an injury, take the cat to the vet or animal hospital right away.  Common locations for fighting injuries include the head, chest and legs.  Be very careful, an injured cat will lash out to try to protect itself, and can cause serious injury. If your male cat is displaying excessive aggression, including hissing, it's possible that he is hyper-territorial. Neutering an aggressive male cat may help correct this behavior and reduce his undesirable aggression.

TL;DR in Indonesian:
Biarkan kucing Anda beradaptasi. Kenalkan hewan peliharaan lain dalam lingkungan yang terkendali. Periksa luka pada tubuh kucing Anda. Pertimbangkan untuk mengebiri atau mensterilkan kucing Anda.