There are many reasons you might want to dump your SVN repository to a flat file : for example to simplify backup operation, to transfer to another server, or to convert your repository from FSFS to BDB or the opposite.
This is actually quite a simple operation :
svnadmin dump /path/to/repository > /path/to/flat_file
Of course you can do the opposite. First create a repository, then reload your flat file into it :
svnadmin create /path/to/repository
svnadmin load /path/to/repository < /path/to/flat_file