How do I begin a discussion? How can I find my class' discussions?

First time member here and currently I am feeling so confused. I have spent at least 45 minutes reading all of the FAQ's and I watches a video tutorial, reccomending I find "content" or "Discussion". When I select discussion, it appears all of the discussions are completelty unrelevant to me. Is D2L Brightspace Community open to the entire public? Or, is this open to Erie Community College Students only? (Erie community college is a SUNY community college located in WNY. If the answer is "yes, ECC only", then my next question would be; Is this discussion / question platform private to each specific class? Can someone please help me understand the sociology aspect behind D2L Brightspace Community? Thanks in advance!!