You can buy a T-Card at nearly every convenience store and you can reload your card on a machine before you pass through the gates to get to the boarding area. The machines are simple to use and even have an English option for foreigners. Nearly every Korean citizen, including kids, have their own T-Card that they use.
Another useful tool in getting around by subway is an app called Kakao Metro. This app identifies the easiest and fastest way to reach your destination by subway. It will even give you how much you will be paying for the trip, how long the trip is including transferring stations, and tell you when the next train is coming. For those who don't have the app, there are also color-coded maps throughout the train stations and on the trains that tell you where to go!
When I first stepped on a crowded Seoul train, I was very nervous. I grew up in a place where the best way to get around was by car. Riding on a subway train every day was very new to me and I didn't know if I could get used to it. When the train began to go for that first time, I lost my balance and stumbled backward! I had no idea it was going to take off with so much force! Luckily, my friend caught me and I was able to find a handle to grab onto. I am still not used to the sudden launch of the train so the handles have become my best friends. If the train is too crowded to find a handle, then my best friends actually become my handle!
Despite that first experience, I found that traveling by train is the best way to travel. I have never been late to anything when I take a train and the stations are always clean no matter how many people rush through them.
