This assumes you have Subversion installed on your local PC. These examples are based on Linux.
Let's say you have checked out http://example.com/svn/repo/testing from the master Subversion repository to /tmp/SVN on your local PC. Create a new file in the directory.
cd /tmp/SVN touch foo.txt
Add the new file to Subversion.
svn add foo.txt
The svn status command will now show that foo.txt has a status of A (ready to be committed).
svn status foo.txt A SVN/foo.txt
You would then commit the new file.