To enable Multiple Account Features in your Gmail you will have to do the following steps.
1.Go to Your Google Account setting.
2. Then under Personal Settings you will see
Multiple sign-in * On/off - Edit
Just click on edit and check the agreement and save the setting.
3. Now just Sign Out and Sign in. You will see at right Corner of Gmail a option in your Gmail to switch the account.
Hope you like our Multiple Account setting for Gmail for any other problem please feel free to contact through comments.