You will need to specify the url to the repository (with the full path the specific branch) that you want to use in "Source Code Management", as discussed in the comments.
You can use polling if you want, which will have check all paths specified for new changes, at the specified regular intervals and trigger a new build when a new revision is detected.
Using a post-commit hook works just as well, and might be even necessary, e.g. if you don't want to constantly poll the repository for changes (maybe because the changes are infrequent), or if you need to specify multiple paths under Source Code Management that are needed for the project, but you don't want to trigger a build for changes in some of them.
The wiki page of the Subversion Plugin provides some nice examples for post-commit hooks, including a VBScript - note that it doesn't use the build trigger url as you did in your script, but notifies the jenkins server of the commit to the specific svn repository.