It is important to know the difference between primary and secondary sources. Primary sources are the first-hand accounts of a topic (diaries, letters, law-texts, photographs etc). Secondary sources are about the topic (articles by academics on historical documents etc) and add a layer of interpretation and analysis. You want some of both.
Make sure you learn the principles of academic integrity and how to cite your sources according to the right citation style. University of Iceland uses Turnitin which enables users to spot plagiarism.