Now that you have created your groups, you need your students to join them. Remember that Edmodo is a secure environment for your students, but you need to take care to follow the steps to ensure the integrity of the groups is maintained.
If you have younger students, or a large class, you may want to enlist the help of an aide to get your student accounts started. Students create individual accounts at http://www.edmodo.com.
Have students take these steps to create an Edmodo account.