To switch accounts
Gmail displays conversations and messages from one Google Account at a time. If you have set up more than one Google Account on your device, you can easily switch between them.
From your Gmail Inbox, tap the Accounts icon
on the Inbox header, then tap the account that contains the email you want to read.
NOTE
The number to the right of the selected Google Account indicates the number of unread messages you have in that account.
Tap here to add an account.
Gmail Inbox
Accounts & Labels
Tap here to open a drop-down menu of account choices and account labels.