If you are viewing a message or another label, tap the Back Key until you return to your Inbox.
While viewing your Inbox, swipe the screen up and down to scroll through the list. The icons at the bottom of the screen allow you to navigate within the Gmail Application as well as use Gmail features:
Compose Tap this icon to start a new Gmail message.
Search Tap this icon to search within the Gmail application.
Labels Tap this icon to view your messages by Gmail label.
Sync Tap this icon to sync your Google Account(s) on your device.
While viewing a message, flick the screen left and right to scroll through all of your messages and use the following icons:
Archive Tap this icon to send the message to your archive folder.
Delete Tap this icon to delete the message.
Labels Tap this icon to set labels for the message to help organize your messages.
Mail Tap this icon to return to your Inbox.