Teachers will use Google Classroom to deliver materials, instruction and resources for learning and assessments. It's important that you accept the invitation from your teacher so you can monitor your childs' progress.
Students will be asked to connect via Google Hangout for various conferences. I'd encourage you to watch the conference with your child to ensure they understand the directions. I'll call, but the number might be "No Caller ID"
Google Chat is a room and online discussion. Your child has been added to my rooms. Each room has a discussion thread about various classes. When kids type a question, I get a text message and I'll reply ASAP. This is a great place to start.