Sweden, like most European countries, has right-hand traffic, and you must have your driving license with you whenever you drive.
A driving license issued by an EU/EEA member state is valid in Sweden for the same period of time as it is valid in the country where it was issued, as long as it has not been exchanged for a Swedish license. You may exchange your driving license for an equivalent Swedish driving license if you reside in Sweden permanently. However, driving licenses from EU/EEA states are valid in Sweden regardless of how long the holder is registered in the country, and it is therefore not necessary to exchange an EU/EEA driving license for a Swedish one.
A driving license issued from a non-EU/EEA member state is valid in Sweden if it is valid in the country where it has been issued, as long as it has not been exchanged for a Swedish license. However, it is not valid in Sweden if you have been registered as a resident in Sweden for more than one year. Thus, a non-EU driving license is generally valid for just one year.
A driving license issued outside the EU can generally not be replaced by a Swedish driving license. The only exception to this is driving licenses issued in Switzerland and Japan.