Once you've arrived in Sweden and received your residence permit, you should register at the Swedish Tax Agency – Skatteverket. This has two main functions: it adds you to the Swedish Tax System and assigns you with a unique identification number, a so called personnummer.
Paying taxes is just part of a Swedes daily life. We pay to society and society pays us back through many social benefits.
Your whole legal existence in Sweden will be based on your personal identification number – so make sure to get one and memorize it.