I have been using Edmodo for years now, and I do think that it is a good tool for students to be able to communicate with one another online. It is an important skill for students to have a firm grip of in today's technology saturated world.
When doing some research for a Digital Citizenship Unit I am doing with my classes right now, I came across a really good resource for those new to Edmodo. It is an Edmodo Teacher's Guide that shows you (with screenshots) how to set up and manage your Edmodo classes!
(screenshot from link below)