Gmail displays conversations and messages from one Google Account at a time. If you set up more than one Google Account on your phone, you can easily switch between them.
From your Gmail Inbox, tap the current account (at the upper-left corner of the Inbox header), then tap the account that contains the email you want to read.
The number to the right of the selected Google Account indicates the number of unread messages you have in that account.
Accounts
Tap here to open a list of account choices and account labels.