You can see a short video about Edmodo here.
Parents can peek into Edmodo if their students will give them the necessary access code. A document that might help you is below, ready for you to download.
Please note that our sharing information about Edmodo with you is not intended to imply that you should become more involved in the management of your student's school work. We want to foster independence, resilience, and responsibility in your students, and at the upper school level, those goals are rarely furthered by having parents stand over students to make them do what they should do.
Some of your students' teachers will use websites (weebly) instead of Edmodo, or along with Edmodo. I am confident that your student will quickly know which place to look for what. If you are confused, your student can help you, I'll bet.