Info in English: www.nts.go.kr and 2-397-1440 or 2-2076-5711.
There is a goods and services tax of around 1.5% on purchases. Sometimes it is added to the bill, and sometimes it is included in the price.
There is a provincial (4-5%) and national income tax (3-4%). Only Canadians should have income tax deducted from their paycheques in the first two years of working in South Korea. Employees who have only employment earnings to report do not have to make income tax returns in Korea. The onus is on the employer. Be sure that the employer is deducting tax properly--if you have questions, you can consult the tax office. However, you may wish to make a return and claim deductions. There is a small sales tax rebate.
Make sure your employer has registered you with the national pension plan and is deducting pension payments. This is your money for the future. In most cases, the fund can be paid back in cash or transfered to your home country's pension plan.