Over the years, NUS Libraries has acquired a collection of primary sources helpful for the study of Singapore history. Those primary sources are mainly copies of records kept in archives around the world (e.g., National Archives, U.K., U.S. and Australia).
They can be in various formats (i.e., print, microfilm or electronic).
The National Archives, U.K. has produced animated guides to help people understand archives. This guide entitled "How the records are arranged" shows how records are classified in the National Archives, and explain reference codes.
Another interesting quick guide: "The records we hold"
For more videos, see The National Archives, U.K. website : Quick animated guides