Are you visiting Norway and staying for up to 90 days? Then you have to apply for a visitor's visa (Schengen visa). You can apply for a visa at udi.no.
You can find out how to extend your visitor's visa at the bottom of this page. A visitor's visa does not give you permission to work in Norway.
How to obtain a guarantee for a visa visit
How to apply for an extension of a visitor's visa
If anything happens requiring you to prolong your stay in Norway or the Schengen area beyond the expiry of your visitor's visa, you can apply to extend your visa.
Do you have a visitor's visa (Schengen visa)?
If you do, you can travel freely in the Schengen countries for as long as your Schengen visa is valid. You must apply for a new visa if you leave the Schengen area and your visa does not cover more entries. Apply at udi.no.