The Field API is major new functionality in Drupal 7 to provide custom data types just like CCK did for previous versions of Drupal. Field API became part of Drupal 7 February, 2009, but there is still plenty of work to do. We need your help, and we’ll help you learn what you need to know to contribute.
The Field API is a great way to get yourself involved directly in Drupal core development. We realize, however, that Field API is a big, new, scary chunk of code that is not the easiest thing to jump into. The Field API team wants to help you get up to speed, so we’ve created the Field API mentoring process. Here’s our promise: If you assign a Field API issue to yourself and take responsibility for it, the Field API mentors will help you learn what you need by participating in the issue and answering questions on IRC.
We’ve created a Field API contributor page at drupal.org that describes (most of) the open issues and their degree of difficulty. If you want to grab one but have some questions about that part of Field API, ask about it over at Field API: What do you want to know? and we can add it to the documentation.