enroll vs. register

sometimes the two words are changeable?
i read the definition of the two words in dictionary which confused me a lot…
it took two days to enroll/register the new students.

two hundred students were enrolled this year.

“Enroll” means to register as a student or as a member of a club or institution.

“Register” simply means to enter into an official list.

You can both register as a student or enroll as a student. In the United States, you have to register your gun with the government (if you have a gun). You cannot “enroll” your gun, because it is not a person who is a student or member of an institution.

Also, ‘enrollment’ tends to be a more general description, while ‘registration’ may be a more specific process. Therefore a statement like ‘Enrollment at ABC University requires registration in person during the week of September 1-7’ is not odd.

oh. got it now.
Thanks a lot.