1.- How to send a message to a classmate through Google Classroom?
To send a message to a classmate you can do it through the hangouts chat by just entering the email of the person you are sending the message to.
2.- In the Gmail email, what is the difference between the Updates Tab and the Forums Tab?
The Updates Tab sends important notifications to your email, such as a notification about a grade or a message in your course.
The Forum Tab only sends notifications about the groups in which you are enrolled and participating depending on your class.
3.- How can I stop receiving email from all the forums?
The information of the forums will arrive to your email automatically once you are enrolled and start participating, you can organize the tabs of your email in a more efficient way through the following steps.