As a teacher, one of the first things you need to do in Korea, is get your bank account set up. Luckily, your school has provided you with a co-teacher whose main directive is to help you get settled in. The assigned teacher will pick you up from the bus, and take you to the immigration office to apply for your Alien Residence Card (ARC). Depending on the time of day, they will also make sure introductions have been made with the Principal, Vice Principal and at least a few of the teachers at your school before taking you to your apartment, and letting you unpack (if you arrive in March, make sure you ask how to use the heater before they leave).
From the date of application, it can take roughly 3 weeks to get your ARC and until then, there won't be a lot you can do. The ARC is needed for EVERYTHING. It is possible the person processing the application might give you your ARC number, which is helpful for setting things up online, but just be aware, most places will want to see your physical card to do bank accounts, mobile phones, internet, cable TV or utilities (if your school doesn't have an account for your apartment).
Back to your bank account. You will need the following:
From there, you have to physically go to the bank to set up the account. It can be time consuming, and there are forms to fill out, which your co-teacher can help you with if you don't read Korean. The teller will highlight the important parts for you, it might take between 15 minutes to an hour depending on your teller, then bang! You are walking out with a new bankcard and bank book ready to spend the money you haven't been paid yet.
Why? Because local branches only give limited access to banking facilities. It is the difference between having a card limited to EFTPOS and ATM withdrawals, or one that can be used for online shopping, travel (T-Money), organizing your holidays, international transfers (you still have to ask the bank to set that up), and everything else we take for granted with our regular bank cards at home. Only an account from the Main branch can do this for you. Further, by going to the main branch in the first place, you won't have to cancel your accidental local account (including bank book and card) which also means changing account numbers with your school and anybody else who is set up for automatic payments.