People write for many different reasons - to inform, entertain, persuade, mislead, satirize, describe, etc. and the quality of the information can depend on the reason it was written or shared. Information changes as new facts, data, and knowledge comes to light. In an academic assignment, it is important to use information that is reliable, accurate, objective, and up-to-date. You will need to evaluate each source you locate, to determine if it is something that will support or contradict your thesis and/or topic. You will look at more sources than you need, and that is okay, and encouraged! The more sources you read, the more informed you are about the topic and can pick the best resources for your assignment.
The video below, created and produced by the University of South Australia Librarians, provides tips on evaluating information using the C.R.A.A.P. test.