Reading
To read a message, simply click on the active link in the From or
Subject columns. From within the message you can go back to
the Inbox by clicking on the icon in the upper left:

You can
also get to the Inbox by clicking on the Back to INBOX text all the way to the right. Next to it you will find arrows
to scroll
through to the next or previous message.
Deleting
You can delete a message while it's open by clicking on the "Delete"
text on the upper left of the message. From the Inbox, put a
check in the box on the left of the message line to select it. Then
click on the Delete text. You will notice on the right, above the
messages, two links for Hide Deleted (or Show Deleted depending
on your default setting) and Purge Deleted. If yours reads Hide Deleted, change your setting to Show Deleted. This means that when you delete
a message, you will still see it, but crossed out. By clicking on Hide
Deleted, you will no longer see messages to be deleted. Regardless
of whether you can see messages you've deleted, you have to click Purge
Deleted in order to actually get rid of those messages. Before purging
deleted files, you can recover them by clicking on the check box beside the message and then on Undelete.