You have to make sure that you are in the 'News/Activism' Forum, then click on 'Topics'. Click on a topic you want to be displayed in the sidebar, when that topic's threads are displayed, they will be a note saying that you aren't subscribed to the topick, and click on another part of the note to subscribe. When you click where instructed, the note will change to say that you are subscribed, and the most recent threads in that topic will be displayed under that topic's name in the sidebar.
Do not try to subscribe to more than 4 to 7 topics at first. As you subscribe to more topics, fewer threads are displayed for each on the sidebar, when you reach a certain point, no more topics will be displayed.