Users community
The majority of people are users. Asking developers to answer all the questions from each and every user is unreasonable. That’s why we need user communities to share the high-level tips about the user experience. The first place to go is the official page.
When you have scoured that page, and you still are lost, continue to some others. The discourse site is full of interesting user and development questions. They also include announcements about new releases. You can ask your own questions, please be civilised. The site is well organised and has a lot of activity.
The site is https://discourse.gnome.org/
If you want to use other means than web pages, you may be interested in IRC channels and mailing lists. You can find options on the community page maintained by the GNOME foundation.
If you do, there are several choices to use IRC in GNOME. Polari is one of the better to find IRC channels related to GNOME. To download Polari, you can use the built-in Ubuntu software installer. The developers uses GitLab, to develop and you can find a flatpak version on their GNOME project page.
For other places, where you can find more information and discussions, there is also a Reddit group for the more active discussions. They are also more spread on users and developers.
These are probably the first places to go for more information and help when you have user questions about GNOME. The GNOME wiki is a comprehensive source of information.
Developer Community
Developers have long used mailing-lists to keep the conversation going and they still are using them. They are using GitLab to keep on top of the development but many times they need another forum to plan new features and float new ideas. To follow the code and issues go to their repository. They have many sub-projects so you can focus on a special detail.
https://gitlab.gnome.org/explore/groups
The best place to find the mailing lists are on their official site. You can see that this contains GNOME and related applications so choose before you join.
The list is long and includes special lists for planning, applications and announcements. There are also many lists for documentation, where you can get experience and create a good reputation in the community. The most powerful part of the mailing lists is that you can scan the old messages to see how they have arrived at the current solutions. You can then also avoid asking questions about bugs and decisions that has already been answered.
Question Sites
To ask questions, it is a good idea to go to the right site, Stack Exchange is a good idea for this. The [gnome] tag has several thousand questions you can look through.
https://unix.stackexchange.com/questions/tagged/gnome
A more active site is ask Ubuntu, they have over 8000 questions with the GNOME tag. They also have many tags with with part gnome.
https://askubuntu.com/questions/tagged/gnome?sort=MostVotes&filters=NoAcceptedAnswer&edited=true
As mentioned earlier Reddit is a great place to discuss issues and get comments. This is moderated by the GNOME foundation themselves so will be clean and insightful.
If you are developing your own applications or extensions, you have more places where you can ask questions. Notice that if you are building an application, it is good to look for Electron as this creates an application that can run on GNOME, and other platforms. There are many other ways to make applications for GNOME but JavaScript has risen to the top for simple ones that are not heavy on CPU resources. Stack overflow is your obvious friend in this regard.
Conclusion
When you start using GNOME, you have a lot of good documentation to follow. Sometimes, it is nice to ask a question about your particular problem. This is best done on the wiki or other forums where helpful folks are usually prepared to listen and send you suggestions. Remember to give back to the community by answering questions that you already have the answer to. If you are developing, you can many times go to the sites that handle JavaScript or whatever other programming language you are using.