If you want to contribute actual changes to the Drupal software, you have to do it through patches. Patches are a kind of text file that describe the changes in a way that lets them easily be applied to the official code base. To create them, you have to jump through a couple of hoops, especially checking out Drupal head from CVS and creating the actual patch from the changes you made.
Contrary to popular belief among the developer community, creating patches is not easy for some. Using the text-only interface of the command line is a big hurdle for the more visually oriented. I finally found a way to do this CVS-checkout-and-patching thing without using the command line but through a free app with a graphical user interface.
I'm sure it’s way more elaborate and slower than through the command line, but this works for me and it might for you, too. Here's a slideshow that walks you through the process, best viewed on Slideshare as it will show the slide's notes there, which you'll need to make sense of this.