Special:Newsletters provides a list of newsletters -- see http://newsletter-test.wmflabs.org/wiki/Special:Newsletters
Currently the sorting is... unclear. This is not very important when we have only four newsletters for testing purposes, but in a real scenario sorting matters, and a lot. Maybe one day we will have categories of newsletters, different ways of sorting them and what not. But let's just aim to have a logical first step good enough for a first release.
Proposal:
# Newsletters the user has subscribed to go to the top, followed by the rest.
# Within subscribed / non-subscribed newsletters, those with more subscribers go to the top.
This sorting doesn't need live refresh when the user changes their subscriptions. Whenever the user reloads or visits the page again, the table wll be updated. Live refresh would create jumps that might confuse the user. Imagine that you are subscribed to a newsletter with 5 subscribers, click unsubscribe kind of for testing purposes, and then the entry "disappears", being dumped down the list.