From a Home screen, navigate: Apps icon > (Google) > Gmail .
If unavailable, swipe up from the center of the display then tap Gmail .
From the appropriate Inbox, tap the circular icon to the left of the message(s).
Message is marked for deletion when the icon changes to a check mark.
Tap the Delete icon (located in the upper-right).
To delete several or all messages at once, refer to Delete emails & recover from Trash and click Computer then choose the desired option. This process can't be completed from the mobile app.