Primary sources provide raw information and first-hand evidence. Examples include interview transcripts, statistical data, and works of art. A primary source gives you direct access to the subject of your research.
Secondary sources provide second-hand information and commentary from other researchers. Examples include journal articles, reviews, and academic books. A secondary source describes, interprets, or synthesizes primary sources.
Tertiary sources, also called a reference work, is a source that gives an overview of information gathered from primary and secondary sources but does not provide original interpretations or analysis.