Press the elipses (...) to bring up the repository explorer.
Right click to Create Folder...
Add the text /trunk to the root svn url and press OK to create your first commit.
Repeat the Create Folder... process for the folders /branches and /tags.
Select the new trunk folder and press OK.
Now add the /name of your project or library to the root svn url/trunk, type a commit message and press OK.
==> You now have your first commit of your project!