Why did the Labour Party win the last British general election?
You should begin by doing some general reading in the field.
Most university courses involve some sort of extended writing assignment, usually in the form of a research paper. Long after you leave college, you will continue learning about the world and its vast complexities.
Papers normally require that a student identify a broad area of research related to the course, focus the topic through some general background reading, identify a clear research question, marshal primary and secondary resources to answer the question, and present the argument in a clear and creative manner, with proper citations. There is no better way to hone the skills of life-long learning than by writing individual research papers.
There are, however, gradations of primary evidence.
The best sources are those in original languages that are linked to persons directly involved in the event or development that you are researching.