How To Introduce A New Kitten To An Old Cat?

I have a four year old cat, I’ve been thinking of getting another kitten for awhile now. My boyfriend and I both work full time as well as going to school full time so we don’t get home at the same times, which makes it hard to play together sometimes. But he would like a new friend to play with him and me since my other friends aren’t around anymore, but I’m worried about how will the new kitten react? And what should we do if they fight or whatever?