A primary source is a document or object that was written or created by someone who was a participant or witness to the event. Examples of primary sources include diaries, letters, speeches, autobiographies, news footage of an event as it happened, or artifacts. (Yes, artifacts, such as pottery, or a quilt.) Ask yourself, "Did the writer or creator witness or experience the event?"
CCGA librarian Lynda Kennedy has a handy chart that will help you determine if your document is a primary source.
A secondary source is not a first-hand or eyewitness account. This source is one step removed from the primary source. It's written after the fact. Think of a secondary source as an interpretation or analysis of a primary source. A journal article may rely on primary sources, but the article itself is a secondary source. An author who studies the speeches and diaries of a subject, and then writes a book, is creating a secondary source.
So what's a tertiary source? It's the source such as a catalog, bibliography or index that leads the researcher to primary and secondary sources.