It is sometimes needed to add files to the English files (eg. adding a new appendix), and it is initial for translations (adding translated files). To add a file you need to put that file to the proper place, where you want it to be.
To add a file, issue the following command:
$ svn add file1 file2
This only schedules the file for addition. To complete the addition of the file(s), you need to do a commit, as described above.
Before adding new files, you should choose the new file name carefully. There are some limitations to file names, because the automatic file name -> entity name conversion.