Hi there, it is scary being diagnosed no doubt. To begin with you are probably on a fixed amount of insulin and the goal is to match the number of carbs you eat to the amount of insulin you have been told to take. After a while doing that they may well get you to start adjusting your insulin if you want to eat more or less.
When I was diagnosed I switched to diet soft drinks and cut any carb based snacking between meals to try and simplify things. If I was hungry between meals and needed to eat something I chose things which were low in carbs. Raspberries for example are really low in carbs, as are walnuts. Cheese and meat are also low carb along with most vegetables(not potato or anything with sweet in the name
. These things won't spike your blood sugar, though a diet based primarily on cheese might be less healthy for other reasons. Tasty though!
There are many more subtleties but to begin with that worked quite well for me.
As for meals themselves, I would weigh the carb bit of my meals, so the cereal/bread/pasta/rice/potato/etc so I knew how many carbs I was taking with a meal. I was told to test using a blood glucose meter before each meal and before bed, if you do that you should be able to see what effect the carbs you eat have. So if you look at the difference in the number before breakfast and the number before lunch that will show you what effect the carbs you had at breakfast time had. If your blood glucose is a lot higher at lunchtime then you had too many carbs for the insulin you took at breakfast and if you are lower at lunchtime then maybe you should have had more at breakfast to match the insulin. It will vary day to day because of any number of factors, so you have to look over a few days to try and spot a pattern.
You may have lost weight quickly before you were diagnosed, that is one of the symptoms (I think more for type 1), and some people put that weight back on once they start taking insulin. I lost about 2 stone in about 2 months before I was diagnosed last October but I have kept that off. There is no fundamental reason why you would put on loads of weight if you remain on insulin, it is still down to the amount of food you eat.
I am about 6 months ahead of you so I am still learning as I go, but it does get much easier.