The words “several” and “severally” sound similar but mean different things and are used differently.
Several means many or plenty in number.
Example: “There were several vehicles involved in the accident”. That sentence says that many vehicles were involved in the accident.
Severally is another word for: separately, individually, or turn by turn.
Example: “The students were responsible for their registration severally”. This means that the students have to carry out their registration activities individually.