This Multi-Trading Service supports trading of more various digital assets other than just Bitcoin, Ethereum and Ethereum Classic, which are already supported by Korbit. Therefore, if you are a level 3 or higher member of Korbit, you can take advantage of the service without the hassle of using a foreign service to do buy and sell digital assets.
I've not used the exchange, but with some google fu I've managed to piece together the following:
You need a Korean bank account, in your name, to use Korbit.
Level 3 means you've verified your account by sending in a scan of your diver's license or equivalent.
If you browse the Korbit site you see that the only fiat that is supported, for the listed pairs, is the South Korean Won. It's a reasonable guess that the same is true to for the currencies that are available upon verification.