HELP ASAP W/ TWO CATS

I have a 1 year old male (neutered) who has been living by himself (as the only cat) with me and my family. Just 2 days ago, we brought in a 3 month old male kitten, Boots. (not neutered, but will be neutered in August) . Obviously, Jet responded by hissing. It has gotten better. They "fight" while Jet tackles Boots and he tackles Jet. They hiss while playing occasionally, and Jet bites under Boots's neck. I am afraid he will get hurt. I am not even sure if they are "fighting" or just playing. I know their relationship will take time, but I do not want any of them to get hurt,
Boots has her own food/water, and litter box.

Is the biting under his neck okay? Boots doesn't seem harmed after playing w/ Jet.

Thank you.

It is really rare for cats to just get on.. they really need to be introduced slowly and carefully.

This is a really good article with advice on how to go about it:  [article="32680"]How To Successfully Introduce Cats The Ultimate Guide​[/article]