There is no need to login to Google Classroom if you are using a school issued device (Chromebook or iPad).
On the Chromebook, you are automatically signed into all Google apps when you log onto the Chromebook.
On the iPad, when the device was setup, you were already signed into all Google apps.
If you are using a personal device for your school work, you WILL need to sign into Google first. Please visit the page link below that shows you how to login