No reason to be sorry . . . there is nothing worse than going full-force into things blindly, IMHO. A non-condensed version of the book would probably have more explanation (I don't like the idea of being pressured to buy things from the doctor!). Might at least one of Dr. D'Adamo's books be available in your library? But, even at that, the explanations may not be satisfactory; many have certainly found reason to criticize.
A very short version is that different environments allowed the different blood types to flourish and part of those environments was of course the food. Presumably the effects of "avoid" foods is very gradual for most . . . which is why most of us do just fine until we hit 60 or 70 and then start to fall apart.
As with so many things, the proof of the pudding is in the eating (I'll excuse your pun if you excuse mine!). Give it a try and see if it helps. Not much to lose . . . you can live without cucumbers. (It is yogurt I really have trouble believing causes type O problems . . . I'm an A myself, so can have it.)