If you're brand new to Google Classroom and want to get an overall feel for the features, here are some short GC tutorials by Google.
If you want to customize the stream with announcements and such, check out the 2 minute video!
Learn to create a rubric within Google Classroom for meaningful feedback with you students.
If you are looking for simplicity, Karen recommends turning off the stream. This creates less confusion for students. Go to Settings-> General-> Classwork on the stream->Hide notifications
Kasey Bell, author of Shake Up Learning, is a Google Suite Guru! She has a lot more resources on Google Classroom here. She provides clear, easy to implement tips and ideas for integrating Google apps into instruction.
Digging into Google Classroom and all of the features can be a black hole! But if you're wanting to dig deep, here are FREE cheat sheets for teachers AND students that she provides.