Learning a language is equal to fill up an empty pool with drops of water, one after each other and as soon as possible. Once you stop filling, the water you have collected in the pool begins to vapourize. In other words, the language skills you've gained begin to weaken. Here's the first drop; unit one. Start doing the exercises just now and never stop until you feel you've filled up your pool. No doubt you will need many other books to study, too. Don't forget! Every work is difficult at the begin ing. However you get a great pleasure when you discover that you have overcome it. After that you do it as if it is one of your past time activities.