David Godman is the best "interpreter" of Ramana's teachings (in English), editor of Be As You Are: The Teachings of Sri Ramana Maharshi. Don't skip the Introduction. Its 244 pages include a glossary and index. A good place to start.

The late Arthur Osborne was a western student of Ramana, and edited The Collected Works of Ramana Maharshi. Not a lot was written by Ramana himself, and Osborne explains much about what was. The Preface repays reading. The 192 pages include glossary and index. Ramana wrote in Tamil, and many references are to Vedanta.

These are good preparations for Talks with Sri Ramana Maharshi (the major source for his direct teachings) some 650 brief transcribed Q-and-A on many topics (with students or with visitors) over about four years (in late 1930's). 683 pages, with extensive glossary and index, it is best read after the above books. A thorough bibliography at the back will lead you to many other books, of many sorts, to follow with.