MS Essentials is just the underpinnings of all the various Windows Live tools (Mail, Writer, Messenger, etc.). Without MS Essentials you could not have Windows Live Mail.
As for where the "About" command is, it is under a pulldown command. That pulldown menu you are probably not noticing, as it is a small down-arrow.
With WLMail open, notice the four tabs across the top (Home, Folders, View, Accounts)?
Notice the menu sort of icon to the left of the Home tab?
Notice the little down-arrow also there? That means there are selections under that selection.
If you click anywhere on that menu (you do not have to click on the down-arrow, just anywhere on the tab).
There you will see the commands: New, Save, Print, Import messages, Export email, Options, About, and Exit).
That is the "About" I said you'd see when you select the pulldown command.