What type of material is it?
Who is it for?
You want to make sure that your source is relevant to your research project or paper.
Relevance depends largely on CONTENT. Careful reading and note-taking are the best ways to determine a source's appropriateness for your topic.
Other points to consider:
Different types of sources can be used for different reasons to support your research. It is important to know the components of each in order to effectively incorporate them.
Scholarly - Scholarly journals are generally peer reviewed, that is, their articles are read and evaluated by experts in the field under consideration. They generally include signed articles, a statement of the author's credentials or academic affiliation, and a bibliography. All of these attributes help make the source more reliable.
Popular - Popular magazines, such as Newsweek, are generally intended to reach a wide audience. The articles that appear in them are generally not peer reviewed and usually do not contain a bibliography. The reliability of popular sources is thus generally regarded to be below the level of scholarly sources
Primary - Primary sources in different disciplines mean different things.
In social science courses, primary sources refer to books or articles that provide original research or reports.
In history courses, primary sources refer to sources that were written during the time period (e.g., newspapers from the time, diaries, letters, etc)
In literature courses, this often refers to the work you are reading (a novel, poem, etc)
Secondary - These are books or articles that summarize, evaluate and report on primary research.