I'm in the discussion section and there is a red dot to the left of the topic. What does this mean?
Angela, can you include a picture?
It is probably the "unread icon" (see Canvas documentation here: How do I use the Discussions Index Page? under View Individual Discussion item 8). Canvas documentation says it is blue. In our branded instance of Canvas, the dot is black. Yours is red because of your institution's branding?
The answer provided by Tasha Biesinger is correct. Also, as you'll see in the link that Tasha provided to you, near the bottom of that Guide, I posted a question asking the Canvas Docs team to please explain this dot ... as I, too, could not find any information on it back in early July. Hope this helps.
The red dot on the Community Following section also means similar in terms of newly added comments/messages etc eg
Retrieving data ...