Please see the following articles to learn how to create assignments of CK-12 materials in these supported LMSs.
How to Create Assignments in Google Classroom (No LTI key/secret needed)
How to Create Assignments in Canvas
How to Create Assignments in Schoology
Installing the CK-12 App in Your LMS
Schoology
Installing the CK-12 App in Schoology - Enterprise Version
Installing the CK-12 App in Schoology - Basic Version
Canvas
Installing the CK-12 App in Canvas
Safari Montage
Installing the CK-12 App in Safari-Montage