Using the Import Subversion feature copies all the selected files to the repository. In addition to storing the files themselves, Subversion identifies each file with a revision number and an import message. The revision number is generated by Subversion and incremented every time a group of files is added. It is especially useful when searching through a file's history.
The import message is specified by the user and is actually optional. That being said, it is important to set meaningful import messages when adding files to a repository, as it will make it easier for you to identify what these files are, the state that they are in, and the reason they were added to the repository when performing future searches.
While these steps have led to a successful import, you may be wondering why nothing changed in the plugin directory. The reason is that the import process only makes copies of the selected files to the Subversion repository. An additional step, called the checkout process, needs to take place to start keeping track of changes and file history.