Answer
Article: An article is a nonfictional composition on a specific topic (stated in the title) about something you have experience or expertise in, or that you have researched.
It's presented in an unbiased manner and strives to prove or accomplish its theme. If an opinion is given, it should be based on knowledge. An article has a lesson or point to make and a conclusion. It's goal is to inform and/or entertain. An article is more formal than a blog, and is normally a minimum of 250 words in length. Feedback comments are accepted.
Blog: A blog entry can be whatever you want it to be... it's a personal journal of rants and raves, your opinions or ideas on any topic, or it could be just a note about your day. A blog post is an opinion, therefore biased, can be of any length, and research is not required. it's less formal than an article. Comments are accepted.
Forum Post: If you want to have a group discussion with many members on any topic of general interest, post it in the CS Forum.