To add another email account to Gmail, simply do the following:
1. Go to 
Settings > Personal > Account > Add Account
2. Touch the type of account you want to add. You may be able to choose from choices like ‘Google’, ‘Personal’, or ‘Work’.
3. Choose “Google” if you want to add your Google Account. When you sign in with a Google Account, all the email, contacts, Calendar events, and other data associated with that account are automatically synced with your device.
4. Follow the on-screen instructions to add the account.
To change the settings of any of the accounts you added, follow these steps:
1. Open the Settings Menu on your device.
2. Under ‘Personal’, touch ‘Accounts’ and select your account. If you’re using a Google account, touch Google and then your account.