The most important aspect of any Apache project is collaboration, so an essential starting point is to join the relevant Atlas mailing lists
The "dev" list is where potential changes, design discussions & anything relating to building Apache Atlas can be found
This can be fairly technical so we also now have a "user" mailing list which is ideal for newbies to the project or those who want to avoid the technical details about Atlas's implementation and just focus on using Atlas to deliver business value
There are replicas of these lists available via gmane.org, but this is not supported by Apache, and the site itself has been in somewhat of a flux recently. If interested go to "news.nntp.org" in a newsreader such as Thunderbird and search for groups under "gmane.comp.apache.incubator.atlas"
Note that these mailing lists will be renamed in the coming weeks/months to support the graduation of Atlas to a top level project
Finally when interacting with the mailing list, note that the EZLM mailing list server doesn't support all mail formats. In particular it has a dislike to HTML only email, so try to send a plain text (text/plain) or at least in multipart. Generally gmail, outlook, lotus notes seem fine, but IBM verse will fail and posts simply get ignored as they are not posted.
The Atlas JIRA is where issues are tracked. A new issue can be opened if you find a bug or hit a problem with Atlas, and this is also one way - in addition to the list - of finding out what code changes are being proposed or going in. Any design discussions will probably be oriented around a specific JIRA and may link to locations on this wiki, include design docs etc. No permission is needed to open a JIRA account, but if you wish to assign an issue to yourself to work on, please ask in the dev list for contributor authority.
Hopefully you find the content here useful. If you would like to make suggestions for improvement, or even better ask to contribute more content, simply ask on the dev list above.
A good starting point is the introduction to Open Metadata