Some teachers think it's fine to learn a language without a course book and prefer to use materials from here and there, but would you fix a car with random tools you have? Or is it not better to have all the tools from the beginning? Yes, course books are expensive, but they are also an investment in learning. You'll learn faster and more thoroughly because these books build grammar, vocabulary, listening and speaking skills in chronological steps designed specifically for English as a Second Language (ESL) learners. Unless you are naturally linguistically gifted, which few of us are, using a textbook as a core curriculum and adding additional study materials is the most successful way to master a language.

These are the books I recommend for learning general English.