To browse via the web use the ViewVC interface:
http://svn.apache.org/viewvc/qpid/trunk/qpid
Or to browse the source tree directly:
https://svn.apache.org/repos/asf/qpid/trunk/qpid
The source code can be checked out anonymous over HTTP:
svn co http://svn.apache.org/repos/asf/qpid/trunk
Committers can check out the code using HTTPS:
svn co https://svn.apache.org/repos/asf/qpid/trunk
A read only GIT repo is available:
It can be cloned with
git clone git://git.apache.org/qpid.git qpid
or
git clone http://git.apache.org/qpid.git qpid
and then git pull will fetch updates.
If you have commit access it is also possible to commit back with git svn dcommit by following the instructions on the GitAtApache page.
When adding files to subversion, it's important that your subversion client is properly setup to the appropriate subversion properties are set. The client can do it automatically by modifying the auto-props section of the subversion config file. Use the contents of:
http://svn.apache.org/repos/asf/qpid/trunk/etc/svn-auto-props