Authentic resources to learn about Buddha's Dharma

I was on a project to read bhagvat geeta and understand it's true meaning by myself (since I was baffled by plenty of commentaries done by others). It's 4th *adhyaya* and I am convinced that this text is written with intention to cover failures of orthodox religion under god's name. The indirect attack on teachings of Buddha(little of which I know) is also evident in some verses. Nonetheless, I want to look for pure knowledge about myself and troubles I am going through and this time it's through Buddha. I am not new to Buddhism but I want to start from scratch,From where should I start? Which is the best book/resource to get authentic information about core of Buddha's teachings?