Natcat120, your cat needs to go to the vet ASAP! He needs to be have the wound properly cleaned and bandaged to prevent infection. An infection in the tail can quickly progress into the spinal cord.
Exactly as @CatPack said, it is very, very important to get the cat in asap to get it wrapped to prevent infection, which can lead to a much bigger problem then you can imagine.
That spinal cord has all the nerves that control so much, and any injury or trauma to it can even cause incontinence, permanently.
Call the vet NOW and tell them what's happened. Ask if they can see your kitty right now, and if they can't, ask where the nearest emergency vet is. Not sure if this works like people's fingers getting chopped off, but take the chopped off tail with you.
Unlike fingers, there's usually no point to attaching a severed tail, and it's a much harder recovery for the cat than a simple amputation. Let the tail go but do get the stump attended to ASAP.
Cats are famous for being stoic when it comes to not showing pain. Just because your cat isn't in obvious pain, doesn't mean her/she isn't in pain. And even if he/she wasn't in pain, the stump can get infected, and cause many very bad issues if not seen by a vet. Please get the cat to the vet immediately.
I adopted a cat who was a stray, but got injured and made his way to our house for refuge. He had a very long tail that had been broken about halfway, and he was bleeding. I wrapped him a towel, and got him into the vet. They ended up amputating the rest of the tail all the way up to his rear end. The remaining tail had become infected all the way up to the root. After that he looked like a Manx. He was not my cat officially before the operation, but as I told the office staff: "Once I pay his bill, he IS my cat. He turned out to be a very sweet and loving cat.
To echo the other posters above: GET YOUR CAT TO THE VET NOW!!!!!