To answer your second question: Most to all public companies release annual reports (e.g. 10-K) where they explain what they do and what they are planning to do. To deepen your understanding of other sectors I would recommend reading/skimming a couple of these annual reports. I think this will give you a good start understanding what a sector is doing and also specifically how a company in the sector is doing.
For example, you want to know more about oil? Read some of the annual reports of the biggest oil companies: