You can move to Norway and start working right away, but you must register no later than three months after your arrival in Norway.
You only need to register once, regardless of how long you will be living in Norway. You can also, for example, go from being a student to being employed without having to re-register.
While you live in Norway, you must belong to one of the residence categories described on this page. You may be an employee, self-employed, family member, student, have your own funds, or be employed by a foreign company. If you are a student or are here on your own funds, you must have insurance.