One of the first things you will want to do is establish a safe place for the female kitty. This is like her special place. The newcomer will go in another room.You can introduce them to each other, one on each side of the door, while giving the two of them some treats. This will show them that being around each other is a good thing. Make sure you give the lions share of attention to the established cat. I assume the male you would be bringing in is good with other cats? That's important to know. If after a few tries with the closed door there is not hissing and there is friendly interest in each other, then you can start opening the door a little at a time while doing the food thing. Also, read this article ---
.
. Let me know how it goes!