Below are the links with all the info you need. I have also added some tips that would have saved me a lot of time:
- UDI Application Portal and Service for Foreign Workers: Here on the Application Portal Norway you can register your application for visa; residence permit for work, studies, and family immigration; permanent residence permit; Norwegian citizenship and travel document. In my opinion, these are the two most useful websites – read them carefully and start your application here before doing anything else.
- Your job contract needs to guarantee a minimum 20hrs work every two weeks: Once you have completed your application via the Online Application Portal Norway, you will probably have to book an appointment to see a representative with the Service for Foreign Workers. If you are required to bring a standard job contract to work in Norway to the interview in order to receive your right to stay in Norway, then make sure the contract stipulates that your employer guarantees you a minimum of 20 hours of work over a two week period, or that it states you are hired on a full time basis. There is usually about a month waiting list to get an appointment with this office, they will deny your application if your norwegian work contract does not stipulate a minimum 20 hours of work over a two week period.
- Get on the phone, double check, and be skeptical: I wasted a lot of time and money travelling to certain places based on out-of-date information or simply wrong advice published online. Calling the organisation responsible for the next part of your visa application will save you enormous amounts of time and money.
Easier way to Norway 
Please note that in certain areas once you’ve entered your application in UDI portal it may take up to 3 weeks to get an appointment with the local police office to hand in your paperwork and hopefully be granted the permit. I unfortunately experienced that after 3 weeks waiting, when I showed up I was rejected because I had made a mistake in filling out the wrong application form, so be wise and call them if in doubt as there are several scenarios for you to seek to be a resident, some of them would lead to a payment of up to 5000NOK. I managed to get the mistake resolved there and then but I saw people being sent away who were told to book a new appointment (another 2 or 3 weeks!). Once you got the permit you would need to apply to the tax office for a personal number: it takes 2 to 3 weeks to receive it (mine was wrong so I had to go back another queue for another hour and thankfully the new number was sent a couple of days later), as a result you will need to plan 5 to 6 weeks to have the necessary paperwork to start working.