I agree with the other reviews on this book, it is well written and designed to give clarity and understanding to the subject. I bought "calculus of variations" by I.M Gelfand and S.V Fomin, another Dover publication, and i found it a little confusing in the way it introduces its concepts early in the text. However, the book by I.M Gelfand and S.V Fomin takes the "normed linear space" approach to the subject of variational calculus, which, can make definitions seem abstract. But if you buy this book and read it along side I.M Gelfand and S.V Fomin's book, it gives clarity and then all is well in the world of variational calculus!
I would suggest that you buy "calculus or variations" by I.M Gelfand and S.V Fomin(or another text which you think is suitable) and this text together, since, as stated in previous reviews of this book, there is not a good amount of exercises and problems to get good practice.(but there are enough to totally understand the subject, its just if you need to practice of problem solving).