Below is the image for the Architecture of SQL Server
Basic storage unit of SQL Sever is called as Page. 1 Page = 8 KB.
Collection of 8 contiguous pages is called as Extent. Pages should be contiguous, they should not be separated.
Collection of Extents is called as Files. It is a physical database file.
Collection of files is called as File Groups. It is a Logical Database File.
Collection of file groups is called as Database.