ATLAS-talk is the ATLAS Discourse instance where you can go to get help with all kinds of issues. It offers a searchable interface for old issues, and will check for questions similar to yours when you’re submitting one. It also includes handy reminders about what to include in your posts when you submit through the web interface.
Please login to ATLAS-talk to enable your account. After that, whether and how you use it is up to you! Discourse is extremely flexible, and has many options for configuration, notifications, and so on (see the intro). If you wish, you can also use the categories as though they are simple mailing lists; each of the major categories accepts questions via email as well as through the Discourse interface.
For more details on how to use Discourse, you can check out the official Discourse forums, or ask a question in the site-feedback category of ATLAS-talk.