Primary Sources provide first hand testimony of direct evidence concerning a topic under investigation. They can include autobiographies, memoirs, oral histories, letters, anything that occurred during the actual time period. In art, it can be a little tricky. If for instance you are studying the copy, Sturtevant's Johns Target with Four Faces (1986), then the 1986 image is your PRIMARY Source and teh original piece it is copying, Jasper John's Target with Four Faces (1955) would then be a secondary source.
