It is expected for the resident cat to be the one doing the hissing.

Introduce them slowly. The best is to bring the new cat into the house and set him up in a single room behind closed doors. They will both know there is a cat behind that door, and they will listen and sniff at them.

When the new cat is calm with his new room, allow the cats to meet, but only while you are there to supervise. Don't take the new cat OUT of the room , allow the resident cat to enter the room, at least for the fisrt meeting or so,

They will settle in as long as you are willing to allow them to do normal cat routines....they will hiss, and growl. They will posture and follow one another around. And they might even avaoid one another. But MOSTS cats WILL adjust.

Good luck and have fun with new kitty.