I will answer your question one by one:
The bolded tile refers to the tile on the square. That is the next square round the edge.
The bolded it refers to those tiles which are not in the center.
The next step is given by looking at A. C should not be clockwise to A, then we have 2. Next, we look at C, D should be clockwise to A, so this is okay. Looking at D, E, F and G all of these are okay, but when we get to H it should not be next to 0, so we have a score of 4. We add 1 because B is in the center to get 5. Then multiply by 3 to get 15. Then add 1 to move B up to the right place, and 1 to move A left to the right place for a final total of 17.