If you are a member, and sign in, you should see a link to join slack at the top of this page. You can also request an invite from webmaster@easternbloc.net.
Once you login, you may join different topic Channels to get notified when new communications are posted.
Make sure to set your notification settings for the Slack App so you get the updates you want.
Learn more about how to use Slack at here or start by watching a video.