> Unfortunatly I have no experience with unified diff and Subversions:(
Subversion is easy.  For starters, you just need to know two commands:
'checkout' and 'update'.  First, check out the current source code:

  svn checkout svn://svn.debian.org/svn/parted/trunk

('checkout' may be abbreviated to 'co')

  If you wish to get the latest code at any time, just change to the
newly created directory "trunk" and issue the command:

  svn update

That's all for Subversion.
The next step is producing code.  Edit the checked out source code.
When you want to create a patch, go to the top level directory of the
source and do:

  diff -Napur . > mypatch.diff

The patch with your changes will be in mypatch.diff then (in unified
diff format, because we specified 'u').

To compile the code, you must do

  ./autogen.sh

once after checking out, and then

  ./configure && make