The link is Blood Sugar 101
Another great resource is a book by Dr. Richard Bernstein, who is a T1 diabetic. Many T1s here follow a version of his way of treating diabetes, which is to greatly reduce the food that causes a rise in blood sugar - carbohydrates. In doing this there is need for less insulin, and mistakes and highs and lows are less drastic. He calls this the "law of small numbers".
Much of Dr. Bernstein's book is available online Read Online - Dr. Bernstein's Diabetes Solution. A Complete Guide to Achieving Normal Blood Sugars. Official Web Site
and would be a good place to start. However, as a T1, your son would benefit greatly from having the book itself handy for reference.
I would extend an invitation to your son to join us here on the forum. It is a great place to be - and among a great bunch of diabetics who have one thing in common - being dedicated to do what needs to be done to gain good control of diabetes, live a long, healthy, complication-free life.
If you would like to post what treatment method your son is on, what his insulin is and when he takes it, if he's counting carbs and what his daily diet looks like, there are T1s and T2-insulin dependent members who could help him navigate this new world of insulin for him.
I'm sorry your son has to go through this (none of us like being diabetic) but we want to encourage you both that managing this disease is doable.