slow down and take a deep breath. this isn't a race. and there's no way in hell you'll learn everything you need to know in one night so just read, take notes, ask questions as you go along and don't worry, we'll help you with this. there's hundreds of us here to help.
with that said, in short what you will do is bring kitty home tomorrow and you will start him on insulin, 1 unit twice a day. don't be surprised if the vet says more because that's what they tend to do because BG (blood glucose) levels are often elevated at the vets but when kitty comes home the levels come down so you should start at no more than 1 unit twice a day.
you will hit walmart and pick up a glucose meter kit (relion micro is economical). if you want you can post your general location (city & state only) and maybe one of us is close enough to give you hometesting lessons. if not, we can show you videos and give you tips and tricks on how to do it.
then you're gonna read about nutrition at
www.catinfo.org and take notes on that over the next few days. then you'll work on getting your testing down so you can safely make a diet change to a diabetic appropriate diet.
and most important of all thru this is that he is still a cat, your cat, so you will stop and watch him a few times, smile at him, enjoy his kittiness, play with him, pet him, and talk to him and i'm sure he'll help you thru a good cry here and there too. :smile: