Easiest way to create a branch:

$ svn copy http://svn.example.com/repos/calc/trunk \           http://svn.example.com/repos/calc/branches/my-calc-branch \      -m "Creating a private branch of /calc/trunk."

Committed revision 341.

Tags are made the same way:

svn copy http://svn.example.com/repos/calc/trunk \           http://svn.example.com/repos/calc/tags/tag-0.0 \      -m "Creating a snapshot of the repository at this point in time and development."