Brandon Simpson Book order

Why does this word have an accent? When do I use ser and estar? Why por and not para? I don't understand the difference between the imperfect and the preterit. The subjunctive? I give up! Do these questions sound familiar to you? If they do, you have the right book. I had the same exact questions when I was studying Spanish. Now, I know them well enough to explain in this book. I have to admit that I don't always know the reason why I use one form instead of another; I learned a lot just from reading and listening to spoken Spanish.