The subway should be fairly usable to foreigners without much instruction - the bus system is another story. During your time in Korea you will encounter hundreds of different street vendors, both within and out of markets. Bargaining is common. There are also western style department stores. Shopping can be a great source of fun in Korea.
Korean food is generally hot.
Occasionally bland or too sweet. You will find some real treasures in dishes like bibimbap, mi-ok gook, bulgogi and kalabi. Luckily for those less adventurous souls Western styled and fast food restaurants abound. Soju, the national drink, and sometimes I think the national pastime, is cheap. This makes for an active, exciting nightlife.