Depends on how you want to contribute, and is you want to contribute to
the Framework and/or
the CMSTesters for PRs are always needed. Currently, in the
CMS there are about 338
open PR's. Of those only about 2 have received testing and the
RTC tag for successful tests.
Reading and cleaning up the Documentation is always a big project and is a good place to learn from and help.
You can always find more opportunities help on the volunteers site
https://volunteers.joomla.org/
PR = pull request, these are proposed code fixes
RTC = Ready to commit, these are patches that have been tested and could make it into a future version.
Each of the
packages in Framework have their own set of open issues and PRs needing testing
I'm currently asking for
help in completing and validating the upcoming alpha Code Standards implementation with PHPCS 2.7.x so developers can have access to the code style autofixers.
https://github.com/joomla/coding-standards/tree/phpcs-2Additionally, there is lots of activity and help needed in Testing Joomla! 3.7.0 Alpha 1 for release candidate status, completing the 3.7 and 4.0 versions of Joomla. We also have need for people to help with improving the unit testing code coverage.
There is also a mailing group specific to the CMS development
https://groups.google.com/forum/#!forum/joomla-dev-cmsWith that being said, welcome to the community; and thanks for being willing to contribute.