A dictionary is the one book every learner should own. Oxford dictionaries and learner's editions are found in encyclopaedia and reference.
Pick a learner's dictionary if English is not your first language, because its simpler definitions and example sentences are far easier to use.
English opens doors to further study and better jobs across India. Read simple books, listen to good speakers and practise speaking daily, even for a few minutes. Regular effort matters much more than perfect grammar in the beginning.
Teachers and learners alike do best with clear goals. Decide whether you need English for exams, office work or conversation, and then choose material that lets you practise exactly that, as often as you can.