How do you participate?
First, you should email content to Professor Sheehan. What exactly it is content? It is an ad that you found online (such as a YouTube video), a posting on a blog relevant to advertising, a news story about advertising or another class topic, anything that strikes you as being something you'd like to share with the class. I'll post your content and give you credit. Second, you should read the postings and comment on them. Anyone can comment.
Check the syllabus for specific requirements in terms of number of postings and deadlines, and number of comments and deadlines.
Also, keep an eye out for items that may be on an exam!