Är du svensk? Går bra att skriva på svenska i detta forum
I'll take it in english. If you have decided to pay taxes it's 30% of your gains. They expect you to provide a complete trading journal with every single trade and transactions (including loans and gifts etc). Regarding mining/PoS-coins you have to pay the same tax as "income from hobby activities/operations".
Easiest way to do it is via localbitcoins, where you can sell directly to other people via Swish (swedish money transfer app created by the banks). Or via bt.cx if you wan't to sell it directly to a company.
