Here is a quick overview of what you need to know to do development work on CLDR.
First, you need to have accounts set up for you on:
Warning: some of these pages get stale. Ask questions on cldr-dev if you run into problems; you or the responder should also fix the stale page.
Next, get your Eclipse environment set up properly.
Run the CLDR tests to be sure they pass before beginning work:
Once you are all set up, be sure to read the development process, for how to handle tickets, when you can't make changes, etc.
Use table below to see where to go next:
Other useful pages are under CLDR Development Site; you can also use the search box. Also, UTS #35: Unicode Locale Data Markup Language (LDML) is the specification of the XML format used for CLDR data, including the interpretation of the CLDR data.