trunk
contains the latest development version of the PFM.
tags
contains the versions tagged at release.
Here is how to create a tag:
http://svnbook.red-bean.com/en/1.1/ch04s06.html
if you use TurtoiseSVN:
select trunk directory, then branch/tag;
in "To path:", enter /tags/<tag_name> (like release-1.7.0)
in log message, enter something useful.