There is a good description of primary and secondary sources for beginners here:
People use original, first-hand accounts as building blocks to create stories from the past. These accounts are called primary sources, because they are the first evidence of something happening, or being thought or said.
Primary sources are created at the time of an event, or very soon after something has happened. These sources are often rare or one-of-a-kind. However, some primary sources can also exist in many copies, if they were popular and widely available at the time that they were created.
All of the following can be primary sources:
Video and film
Published first-hand accounts, or stories
Second-hand, published accounts are called secondary sources. They are called secondary sources because they are created after primary sources and they often use or talk about primary sources. Secondary sources can give additional opinions (sometimes called bias) on a past event or on a primary source. Secondary sources often have many copies, found in libraries, schools or homes.
All of the following can be secondary sources, if they tell of an event that happened a while ago:
Movies of historical events