Simply put, read the Distant interactions section of Plume's documentation. It'll be more up-to-date and more thorough than I am here though this is simpler.
Getting your posts over there
To federate your blogs from your instance to another, it's as simple as navigating to
Getting their posts over here
To federate someone else's blog posts to your instance it's exactly the reverse of the above. This is also how you view a remote profile so you can subscribe to it.