Once click tracking is enabled, an additional link will appear on your sidebar labeled statistics:

This link will take you to a page (under development) enabling more detailed statistics about user and link tracking:

The overview page is a useful place to start. It will show you your most recent messages and indicate how many were sent, how many bounced, and how many were viewed:

The viewed counter is a link to the message detail page, which will show you which users viewed the message:

From the statistics page, the view clicks by url link will display all the URLs you've used in all your messages. On this page, the total clicks per URL will be indicated:

Clicking on the URL will take you to the URL detail page, which will show more detailed statistics for each message:

Clicking on the message link will display the click statistics for this message and clicking on the view users link will show which users clicked this link in this particular message:

The view clicks by message link on the statistics page will display click statistics on a per-message basis (instead of the per-URL basis, as before):

Clicking on a message will then show statistics about all the URLs included in that message:

The link to view opens by message displays the same data as the overview link, except the messages' subjects are not clickable, so this page essentially provides less data than the overview page. Let's ignore it.

This seems to be part of the ongoing development of phpList. At the time of writing, this link displays nothing. Let's ignore it too.