It said that the trade rate for 100CSC is 3,575,000 sP, but how does one go about actually exchanging the two currencies?

You put it in your user shop and price it, then wait for somebody to buy it. Or, alternatively, you can put it in trades and wait for somebody to offer on it.

Do I have to change it to a coin or voucher or something in order to make it an item first?

EDIT: Oh, into gift cards. ok.

Yeah, sorry. ^_^; I should have mentioned that.