Top tip for new SVN users; this may help a little with getting the correct URLs quickly.
Run svn info
to display useful information about the current checked-out branch.
The URL should (if you run svn in the root folder) give you the URL you need to copy from.
Also to switch to the newly created branch, use the svn switch
command:
svn switch http://my.repo.url/myrepo/branches/newBranchName