The student should first know the CommonLit code for the class they want to be registered in. (As their teacher, you can find the code for each of your classes on your "Manage Classes" page.) Students should then go to www.commonlit.org/code and enter the code.
From there, they just have to fill out a simple form. They will need to enter their first name and last name, which will generate a username for their account. They will also need to indicate their grade level and create a password. Email address is optional.
We created a printable handout for students to help them sign-up for and log into CommonLit. Follow the provided link or download the attachment on this article.