Discussion forums are a good place to get support on WordPress related issues. They are also a great place to connect with fellow WordPress enthuasiasts. If, however, you need priority support, it is better to use a premium WordPress support service.
This page lists some of the most popular WordPress forums on the internet.
The official WordPress support forums on WordPress.org is by far the largest community of WordPress users on the internet. When you do a search online about a WordPress problem, you are bound to come across a thread on the support forums from someone with the same issue.
The main downside is that there are too few people helping others. This is why the vast majority of threads created by WordPress users about a problem they are facing go unanswered. Despite this, it still remains a useful archive to search about WordPress.