You can register for iCivics using Clever right from the iCivics site. Visit www.icivics.org/register. Click the "Sign Up with Clever" button.
Follow the prompts for entering your school district and your district login information.
Once you've logged in through Clever, you will see the option to allow iCivics to create accounts for you and your students using information from Clever. Review this information and then click "Allow and Continue". Clever will automatically sync your classes to iCivics and roster your students.