There are a few things you should know about the mailing system in Korea:
1. Mail only runs M-F (typically). Some places it runs on Saturdays
2. Post Offices open M-F 9-6(in my area). This is obviously subject to change
3. You can package, tape, bind, send, and receive mail at your local office. Most of the supplies, except for the boxes, are free.
4. You can always arrange to have your packages picked up at the post office.
Sending packages home is relatively expensive. I just sent a package home that barely weighed 2lbs, and the cost was 32,000 won (roughly $30 USD). I simply filled out a form, detailed the items, and handed the box to the mail handler. She simply weighed the package, confirmed the address, and sent the items on their way. I cannot give you an idea of how long it takes, as I sent the package out yesterday. I will re-post when I send Christmas gifts. I'm guessing it will be around $100USD.
Receiving Packages: It is important to have your address written in English. The format of the address is irrelevant in my experience. Just make sure you have the correct zip code, and all of the information from your ARC. This is what worked for me:
South Korea, Ulsan-si,
Ulju-Gun, Guyeong-ri,
Beomseo-Eup,
(Then insert the address on your building and zip code)
I suggest you write your address in English and send your parents(or whoever) a typed version in Korean. They can print out the Korean address and paste it onto the package. I noticed that my packages arrived faster when I did this. I had some items sent to my school, and some sent to my home. I work 9-5, so I am never home when the mailman comes. He simply leaves a note on my door, and I know it's waiting for me at the post office. I pick it up after work. I go to the teacher's office to pick up packages that have been delivered to my school.
As far as pricing, packages up to 4lbs are around $50 ,and smaller, flat envelopes(depending on how fast you want the items to arrive) can be anywhere from $13-$26. The packages I received took about a week, whereas the small envelopes took about 12 days. This is all through USPS. USPS is less expensive than FedEx, but FedEx is faster, and there are FedEx operators in Korea. I used FedEx to send all of my documents to Korea.
*Please be aware of Korea's policies for sending and receiving certain products.* Echinacea is banned in Korea, so sending any sort of products with this herb will not be allowed past customs.