Because it is an open source project, there are many ways to contribute to WordPress. Some people write code or fix bugs. Some translate WordPress or plugins into their language. Some present at a WordCamp.
My contribution is to volunteer in the WordPress support forum. A weekly calendar task reminds me to visit the support forum and see if I can help solve someone’s problem. I have learned a lot over the years from others sharing their knowledge. Now I try to give back.
The “No Replies” list is a good place to start because those posts do not yet have a response.
One of the pitfalls is replying to a support post that turns out to need more help than expected. These support posts need to be seen through to a resolution because the post has been kicked out of the “No Replies” list, so the likelihood that someone else will jump in to help is low.
It’s a great feeling to help someone get unstuck, and to contribute to the WordPress community.