I was alone on my first day in Seoul and I decided to travel to Seoul through AREX, it was easy and cheap although I had to stand most of the 45-minute travel. I bought an M-Pass for five days which was good for buses and trains around Seoul
For the next 5 days, we mainly used the subway to travel and look for the places we wanted to go. the stations are announced in Korean,English, Japanese and Chinese so it really helped plus it was flashed on LED or TV screens inside the train.
There were also signs of landmarks after you get off so you'll know what exit you'll use

Purchased a subway card ($2.50 USD) and put $10.00 on it. We used it for 5 days and didn't run out. The system is easy to understand and navigate. The cost is much cheaper than other major city subway systems such as Tokyo.