When learning about the past, the term "primary source" refers to objects like documents, letters, diaries, photographs, advertisements or newspaper articles. Almost any print material found in its original form is a primary source. Many primary sources have been rewritten and copied so more people can learn from them.
A "historical artifact" on the other hand, includes primary sources and a lot of other objects. Kitchen tools from a farmhouse, a plow, or a printing press are all historical artifacts. Artifacts can be found almost anywhere and can be helpful in learning about the past.
A "secondary source" is a written summary of the past. Usually secondary sources are based on the study of artifacts and primary sources. The best example of a secondary source is a history textbook found in every classroom library.