If you added more than one Gmail Account on your phone, you can choose to combine all of your Inboxes together. Otherwise, Gmail will only display conversations and messages from one account at a time, but you can easily switch between your different Gmail Accounts.
From your Gmail Inbox, tap the Menu icon , tap the current account, then tap the account that you want to display.
The number of unread messages is displayed to the right of each account label.
Menu Icon
Tap here to open a list of account choices and account labels.