It looks like a letter going into a letter holder. This is where all of your new mail is stored. Even after you have read your mail, it will remain in here until you decide to either delete it or save it to another folder. First make sure that you are in your inbox. You should then see all of the messages that you have available.
Any unread message is marked by a black dot under the 'S' column.
Using your mouse, double click on any message you would like to read. This brings up another window. This new window contains your message. With the mail either highlighted or up in its own window, click on the first button from the left. It looks like a trashcan.