Check with the Korean embassy or consulate in your country for visa and passport requirements. In the United States, see the Korean Embassy website, which has detailed information.
Although a lot of signs in Seoul are written in both Korean and English, you should take a few hours to learn Han-gul, the Korean alphabet. The words "a few hours" are not a typographical error; the alphabet really is simple enough to learn in a matter of hours. This investment of time will be amply paid back in your enjoyment of your time in Korea. You can start learning the alphabet at this website.
We also have a quick reference for the alphabet and a description of the Romanization method we're using.
As you go through the disc, you'll see some Korean words written in English and in Han-gul
like this, to help you get the flavor of the written word. [We're giving you a little extra pronunciation help by putting dashes between the syllables when we Romanize a Korean word.]