Hi @FrancoTorres -- I recommend talking with your Canvas Support at your school. Perhaps they have a system in place to add students. Or it's also possible you have the content in the incorrect course and that students are in a course you should be using.
If you are supposed to manually add students (i think in many districts or universities this is not the case), you would go to People, click the Add+ button and add them by the appropriate method for your school. In my district adding students means using their Login ID.
But the best thing is to reach out to your school's IT/Tech Support to know how it's done at your school.
