Students are not required to use the Common App to apply, however it can save time in the application process. While it is a popular option, it is not the only option for college applications.
Here are some resources to make the Common App application process go smoothly
List of colleges on Common App - https://www.commonapp.org/explore/
First year applicant guide - https://www.commonapp.org/apply/first-year-students
Common App FAQS - https://membersupport.commonapp.org/membersupport/s/