Hey Reet - I think it's awesome that you want to learn more for your boyfriend's sake. I know for my wife it is frustrating to her that she does not understand every little part of my diabetes. I once taught a class on diabetes, and found out that a very simple visual helped people who did not know what diabetes is, so maybe it will help someone in your situation: On a piece of paper draw a circle, to the right of that circle draw a square, and on the edge of the circle draw a triangle. The circle is a cell in the body, the square is sugar (glucose), and the triangle is insulin. Sugar is the fuel for the cell, and the only way for the sugar to get into the cell is through the insulin. Therefore, when we don't produce insulin the sugar in our bloodstream (blood sugar) cannot be absorbed into our cells, and this leads to high blood sugar; and conversely when we take too much insulin it is absorbed out of the blood too quickly leading to a low blood sugar.
The body's organs are constantly throughout the day secreting glucose, and the insulin needed to cover this is the basal rate. When we eat, we flood the body with the sugar ingested (as carbohydrates) and we need to bolus to cover this. Testing the basal rate is as simple as not eating for a defined period of time (usually 6-8 hrs), and constantly testing the blood sugar, which will tell you for this period of time what basal insulin is needed to cover the body's normal glucose secretions. This basal testing is generally done on three or four consecutive days, with a different 6-8 hr period covered on each day.
As for what you can do to help: just be supportive. Asking questions is always good, as it shows your bf that you care and want to understand. You need to realize that our moods will change as our blood sugar either spikes or drops (but don't let him get away with using this to his advantage ;) and be understanding that it sucks sometimes. Oh, and don't tell him he can't eat sugar! haha
Good luck, I hope this helps!!