Opening The Pulse shows you a list of people's posted status messages and notifications of new blog activity, plus any replies to those entries.
You can display the Pulse entries posted by everyone, only entries posted by those in your people list (plus entries to which they have responded), only your own entries, or only unread entries.
When you open a blog notification, you are taken to the user's blog. When you open a status message, you are taken to the user's profile.
You can also work with entries in The Pulse just like posts in communities. For example, you can comment on status messages or blog entries.
Note
If you are an external user (you normally connect to a different system, and are here because you were invited), you won't usually see The Pulse.