Primary is displayed in the Inbox header.
If you have more than one account, you can switch accounts to view
the messages in each Inbox. Tap the Menu icon to select another account or
tap All inboxes to combine and view all of
your account Inboxes at the same time (Primary in the header changes to All inboxes).
Conversations with new messages are displayed with bold subject lines. To read a message in a conversation, tap its subject line text.
The letter icon (or contact photo) next to a Gmail message allows you to select it and choose an action from the icons at the top of the screen.
The Favorite icon next to a Gmail message allows
you to designate it as a favorite message (select the Starred label
to view them).