To follow a space and receive updates from that space in your activity feed, Navigate to the space you would like to follow. Sometimes you will need to click on it's Content tab-- then you can find the "Follow" link at the top right:
Once you click Follow, you can choose to get inbox notifications whenever new content is posted to the space, simply check the Inbox box.
Each space is related to getting assistance or discussing verticals that Relias Learning covers (Administrator & Supervisor Support Portal , The specified item was not found., Relias Learning Events- Impact Nation 2017 and Feature & Content Requests ). You can follow as many of these as you want (there is no limit)!
Some groups also give you the option to Join them. For these you will see a "Join" button right next to "Follow", simply click to join the group!