The default subtab is My Incoming, which is like your inbox. All My Email is a combination of My Incoming and My Sent. There's also My Unread for unread messages, and My Today for just today's messages. Finally, All Incoming is a subtab that only admins see, allowing them to read everyone's email.
Each email has a checkbox on its left that is used to Delete or Mark As Read messages in bulk by ticking the checkboxes of one or more emails, then clicking one of these two buttons. Many messages also have a Go To Lead button if the message is associated with a lead. Clicking anywhere else in the row takes you to the email message.
Simply enter some terms into the search field below the New Email button near the top right and click the Search button. Then, to go back the main list, click the Clear button.
Unsurprisingly, clicking the New Email button takes you to the email composition page. The Body field will be pre-populated with your signature, as defined in General Settings. After filling out all of the fields, send the email by clicking Send.