Prepare a review on the book Animal Farm by George Orwell, clearly mentioning its motive.

I'll start by saying that there is no single, definitive way to write a book review. Various book reviews are likely to share similarities, but some teachers or editors want to see plot summaries while others do not. Similarly, some readers will want your flat out opinion, while other readers do not want that; therefore, my first suggestion is to consider your reader and shape the review around what he or she expects.
Another thing to consider is your attention-getting hook. A good book review is going to grab reader's attention right from the start. If it doesn't, the reader is either going to skip to your concluding paragraph or stop reading altogether. For a book review, I recommend one of three hooks. Use a quote from the book, ask your reader a question, or make a very bold claim that begs for further explanation.
After the introduction, it is fairly standard to walk your reader through a basic plot summary. The key is to keep it relatively short. This will move your reader quickly through the most key components of the plot, the setting, and the characters. Avoid spoilers as much as possible, and definitely don't give away the ending. You want your readers to have a similar experience with the book as you had with it.
After the plot summary, move toward critically examining the quality of the text. There are likely things that the author did well and things that the author struggled with. Highlight those things. Maybe you found a particular character extremely well-written, or maybe you found a particular section of the book that really bogs down due to needless details. Explain those instances.
For the conclusion, don't introduce new concepts, ideas, and thoughts. Reiterate what you have said, and steer your reader toward some kind of action. For a book review, this action is likely one of two directions. Steer the reader toward getting a copy of the book and reading it, or steer the reader to pass on this particular text.