When you are paid 7 days after making a post, you are paid either 100% Steem Power or 50% Steem Power and 50% SBD (unless you decide to decline payout). 
In order to get the 50% of the payout that you received in SBD, you **convert to Steem** (a 3 day process) then **Power Up** using the Steem you received from SBD

*You might wonder why you'd not just get payout 100% in Steem Power if you are going to convert the other 50% SBD into Steem Power anyway. Well, based on different values of the currencies, you may make up to 63% more if you do the 50% / 50% option*